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NASA's Planetary Decadal Survey Vision and Voyages has concluded that measurements of isotopic cometary water vapor, and in particular the deuterium-to-hydrogen ratio (D/H) ratio, are an important tool for unraveling the mysteries involving the origin of Earth's water, and the evolution of our solar system. To support this goal, we have developed, through an internal Jet Propulsion Laboratory research program, quantum-limited superconductor insulator superconductor (SIS) receivers covering the important 500 $-$ 600 GHz submillimeter frequency band. These instruments can detect the (1 $_{10}$ -1 $_{01}$ ) HDO rotational transition, and the (1 $_{10}$ -1 $_{01}$ ) ground state (rotational) transitions of Ortho H $_2^{16}$ O, H $_2^{17}$ O, and H $_2^{18}$ O with exquisite sensitivity. However, given the extremely weak HDO emission and the time-variability of the outgassing processes in comets, expeditious low noise D/H ratio measurements of these sources remain extremely challenging. To address this issue, we investigate the possibility of acquiring HDO, H $_2^{17}$ O, and H $_2^{18}$ O simultaneously by means of a novel dual local oscillator (2LO) down-conversion process, as an alternative to ultra—broadband IF bandwidth systems.

Chip-scale molecular clocks (CSMCs) perform frequency stabilization by referencing to the rotational spectra of polar gaseous molecules. With, potentially, the “atomic” clock grade stability, cm3-level volume, and $4.3\times 10^{-11}$ under an averaging time of $\tau =10^{3}$ s while consuming 70.4-mW dc power.

The pure rotational spectrum of isopropyl isothiocyanate was measured using a supersonic-jet Fourier transform microwave spectrometer in the frequency region of 2–20 GHz. The rotational transition ...

Dunham type parameters obtained from global processing of experimental vibrational–rotational and rotational transition frequencies of 14N16O and 16OH molecules are used for constructing RKR curves of potential energy. Pointwise defined potentials are approximated by expansions in the variable $${{z}_{S}} = (r - {{r}_{e}}){\text{/}}r$$ . Potential energy functions of the abovementioned molecules are calculated nonempirically using the Molpro software. The obtained results are compared with literature data.

Hydration or interfacial water present in biomolecules and inorganic solids have been shown to exhibit a dynamical transition upon supercooling. However, an understanding of the extent of the underlying surface hydrophilicity as well as the local distribution of hydrophilic/hydrophobic patches on the dynamical transition is unexplored. Here, we use molecular dynamics simulations with a TIP4P/2005 water model to study translational and rotational relaxation dynamics of interfacial water on graphene surfaces. The purpose of this study is to investigate the influence of both surface chemistry as well as the extent of hydration on the rotational transitions of interfacial water on graphene oxide (GO) surfaces in the deeply supercooled region. We have considered three graphene-based surfaces; a GO surface with equal proportions of oxidized and pristine graphene regions in a striped topology, a fully oxidized surface and a pristine graphene surface. The dipole relaxation time of interfacial water shows a strong-to-strong, strong, and a fragile-to-strong transition on these surfaces, respectively, in the temperature range of 210-298 K. In contrast, bulk water shows a fragile-to-strong transition upon supercooling. In all these cases at high hydration, interfacial water co-exists with a thick water film with bulk-like properties. To investigate the influence of bulk water on dynamical transitions, we simulated a low hydration regime where only bound water (surface water) is present on the GO surfaces and found that the rotational relaxation of surface water on both the GO and fully oxidized surfaces show a single Arrhenius behavior. Our results indicate that not only does the local extent of surface hydrophilicity play a role in determining the energy landscape explored by the water molecules upon supercooling, but the presence of bulk water also modulates the dynamic transition., Comment: 14 pages, 9 figures

The effect of an external longitudinal magnetic field on the optical free induction decay from a free radical is observed for the first time. The experiments were performed on a rotational transition of the hydroxyl radical, OH (2Π3/2(J = 1) ← 2Π3/2(J = 0) at 83.8 cm-1), using a terahertz free electron laser. In contrast to the results of the experiments with a stable paramagnetic molecule, NO, the observed effect of an external magnetic field on the free induction decay from hydroxyl radicals is more complicated. A longitudinal magnetic field leads to the rotation of the polarization plane of the FID radiation and to an additional modulation of the signal intensity. The angle of the rotation of the plane of polarization is large, in agreement with the theoretical predictions. The observed FID kinetics in the time domain are in semi-quantitative agreement with the modeling. This observation opens an opportunity for the selective detection of weak signals of short-lived reactive paramagnetic free radicals from overwhelming signals that originate from stable non-paramagnetic species by polarization discrimination.

One of the most critical technical challenges in the field of fire safety is detecting the temperatures and concentrations of combustion gases mixed with smoke particles in fire environments. In this study, the absorption lines for the rotational transitions of carbon monoxide (CO) and nitric oxide (NO) were measured in the terahertz range 400–1000 GHz at room temperature and around 340 K. A signal-to-noise ratio of 140 for the absorbance of the J = 8–7 rotational transition for CO gas was achieved. This measurement approach allows simultaneous measurement of the temperature and concentration of each gas by reference to the Boltzmann plot of their absorbances. The temperatures obtained for both gases were consistent with those measured using a thermocouple within the respective 1-σ errors. Moreover, the concentrations derived by this approach agreed with the original gas concentrations within the respective 2-σ errors. Small temperature increases of ∼50 K from room temperature were identified. The accuracies of the derived temperatures and concentrations demonstrate the potential of terahertz spectroscopic sensing for diagnosing combustion gases in fire environments.

In a recent work on line shape parameters for the H2O-H2 [Renaud et al., Icarus, 306,275, 2018] it was shown that this far off-resonance collision system displays strong vibrational dependence. In Renaud et al., calculations were made for bands with one bend or stretch (symmetric or antisymmetric) vibrational quanta exchanged. Water is seen throughout the universe under a vast range of conditions. The needs of the spectroscopic and astrophysics communities include data for water vapor transitions with multiple quanta exchanged. In this work, calculations were made using the Modified Complex Robert-Bonamy (MCRB) formalism for 0–4 vibrational quanta exchanged in the ν1, ν2, and ν3 bands, and the 3ν1 + ν3 band at 13 temperatures from 200 to 3000 K: calculations for more than 100,000 transitions. From these data, the vibrational dependence of the half-width, line shift, and their temperature dependence are studied as a function of rotational transition. The results show a strong and unusual vibrational dependence. The data were used to develop a prediction routine, which is based on theory [Gamache and Hartmann, JQSRT, 83, 119, 2004] rather than ad hoc fitting to a polynomial or other forms. The resulting prediction algorithm gives line shape parameters with much lower uncertainty compared to those from J″ average values or polynomial methods. A line file, based on HITRAN2016, was created for remote sensing applications that study H2O in hydrogen-rich atmospheres.

The starting point for the development of any astrochemical model is the knowledge of whether a molecule is present in the astrophysical environment considered, with the astronomical observations of spectroscopic signatures providing the unequivocal proof of its presence. Among the goals of astrochemistry, the detection of potential prebiotic molecules in the interstellar medium and planetary atmospheres is fundamental in view of possibly understanding the origin of life. The detection of new molecules in space requires the spectroscopic signatures (mostly, rotational transition frequencies) to be accurately determined over a large frequency range. This task is more and more often the result of a synergic interplay of experiment and theory.

The isomerization of the double bond plays an important role in the braking and de-braking of the light-driven molecular brake. Therefore, the Pp-type light-controlled molecular brake system containing the C=C double bond was theoretically studied. Combining the 6-31G(d) basis set, the ωB97XD functional with dispersion correction was applied to implement the (E)-configuration and (Z)-configuration initial optimization. Next, using the 6-311G(d,p) basis set, the relaxed potential energy surface scans of the rotation angle were operated, and then the optimization calculations of the transition states at the extremum high points. Analyzing the stagnation points and the rotational transition state on the MEPs, the rotation mechanism and basic energy parameters of the molecular brake were obtained. Then the DFT computations at ground states and the TD-DFT computations of vertical excitation energy was put into practice at the accuracy of the def-TZVP basis set for the two configurations, and using the natural transition orbital (NTOs) analyses combining the excitation energies and absorption spectrums of the molecules, the electronic transition characteristics and electron transfer properties of light-driven molecular brake were studied. Afterwards, in order to investigate the photo-induced isomerization reaction, the C=C double bond was scanned on the relaxed potential energy surface, and the intermediates of the isomerization reaction was searched and analyzed, thus, the braking mechanism of the light-driven molecular brake was proposed.

Context. The discovery of an extrasolar planet with an ocean has crucial importance in the search for life beyond Earth. The polarimetric detection of specularly reflected light from a smooth liquid surface is anticipated theoretically, though the polarimetric signature of Earth's oceans has not yet been conclusively detected in disk-integrated planetary light. Aims. We aim to detect and measure the polarimetric signature of the Earth's oceans. Methods. We conducted near-infrared polarimetry for lunar Earthshine and collected data on 32 nights with a variety of ocean fractions in the Earthshine-contributing region. Results. A clear positive correlation was revealed between the polarization degree and ocean fraction. We found hourly variations in polarization in accordance with rotational transition of the ocean fraction. The ratios of the variation to the typical polarization degree were as large as ~0.2-1.4. Conclusions. Our observations provide plausible evidence of the polarimetric signature attributed to Earth's oceans. Near-infrared polarimetry may be considered a prospective technique in the search for exoplanetary oceans., Comment: Published in A&A (20 pages, 14 figures, 3 tables). Note added in proof

We examine rotational transitions of HCl in collisions with H$_2$ by carrying out quantum mechanical close-coupling and quasi-classical trajectory calculations on a recently developed globally accurate full-dimensional ab initio potential energy surface for the H$_3$Cl system. Signatures of rainbow scattering in rotationally inelastic collisions are found in the state resolved integral and differential cross sections as functions of the impact parameter (initial orbital angular momentum) and final rotational quantum number. We show the coexistence of distinct dynamical regimes for the HCl rotational transition driven by the short-range repulsive and long-range attractive forces whose relative importance depends on the collision energy and final rotational state suggesting that classification of rainbow scattering into rotational and $l$-type rainbows is effective for H$_2$+HCl collisions. While the quasi-classical trajectory method satisfactorily predicts the overall behavior of the rotationally inelastic cross sections, its capability to accurately describe signatures of rainbow scattering appears to be limited for the present system., Comment: 9 pages, 6 figures (Supplementary Material: 3 pages, 5 figures)

We perform a comprehensive demographic study of the CO extent relative to dust of the disk population in the Lupus clouds, in order to find indications of dust evolution and possible correlations with other properties. We increase up to 42 the number of disks of the region with measured CO and dust sizes ($R_{\mathrm{CO}}$, $R_{\mathrm{dust}}$) from observations with the Atacama Large Millimeter/submillimeter Array (ALMA). The sizes are obtained from modeling the ${^{12}}$CO $J = 2-1$ line emission and continuum emission at $\sim 0.89$ mm with an empirical function (Nuker profile or Gaussian function). The CO emission is more extended than the dust continuum, with a $R_{68\%}^{\mathrm{CO}}$/$R_{68\%}^{\mathrm{dust}}$ median value of 2.5, for the entire population and for a sub-sample with high completeness. 6 disks, around $15\%$ of the Lupus disk population have a size ratio above 4. Based on thermo-chemical modeling, this value can only be explained if the disk has undergone grain growth and radial drift. These disks do not have unusual properties in terms of stellar mass ($M_{\star}$), disk mass ($M_{\mathrm{disk}}$), CO and dust sizes ($R_{\mathrm{CO}}$, $R_{\mathrm{dust}}$), and mass accretion. We search for correlations between the size ratio and $M_{\star}$, $M_{\mathrm{disk}}$, $R_{\mathrm{CO}}$ and $R_{\mathrm{dust}}$: only a weak monotonic anti-correlation with the $R_{\mathrm{dust}}$ is found. The lack of strong correlations is remarkable and suggests that the bulk of the population may be in a similar evolutionary stage, independent of the stellar and disk properties. These results should be further investigated, since the optical depth difference between CO and dust continuum may play a role in the inferred size ratios. Lastly, the CO emission for the majority of the disks is consistent with optically thick emission and an average CO temperature of around 30 K., Comment: Accepted for publication on A&A, 14 pages of main text with 5 figures, and 11 pages of appendices A, B, C, D, E and F with 13 figures

To illustrate planetary atmospheric environment, such as a three-dimensional structure of trace gases, combination of high precision millimeter and submillimeter-wave spectroscopic remote-sensing and an advanced information processing technology is crucial. By combining the open-source radiative transfer code Planetary Spectrum Generator (PSG) and the Python libraries SciPy and astropy, we have constructed the molecular profile derivation tool Planetary Atmospheric Spectrum CALculator (PASCAL), which focuses on analysis of data of Titan observed by the Atacama Large Millimeter/submillimeter Array (ALMA). PASCAL successfully retrieved the vertical profile of an isotopomer of a gaseous hydrogen cyanide (H\(^{13}\)CN) J = 3–2 rotational transition, where J is the rotational constant, from ALMA archival data. Further, it successfully determined that the northern high-latitude region has 27\(\%\) higher column density than the south as seen in the intensity map. In addition, an installed parallelization method succeeded in decreasing the calculation time with its parallel speedup value \(\sim \)20 using 32 processors applying coordinate parallelization.

We have stabilized the frequency of a 3.1 THz quantum cascade laser (QCL) to the rotational transition $J=27\leftarrow 26$ of carbon-monoxide (CO). The achieved frequency stability was $5\times 10^{-9}$ in the Allan standard deviation at 10s averaging time. The absolute frequency of the THz-QCL was determined to be 3097909.4 (0.1) MHz, which agrees to the previous report within the uncertainty [1]. This CO-stabilized THz-QCL has a potential to be served as an unprecedented frequency standard in THz region.

Stereodynamics of cold collisions has become a fertile ground for quantized studies of molecular collisions and control of the collision outcome. A benchmark process for stereodynamic control is rotational transition in He+HD collisions. This process was recently probed experimentally by Perreault et al. by examining quenching from $j=2$ to $j'=0$ state in the $v=1$ vibrational manifold. Here, through explicit quantum scattering calculations on a highly accurate ab initio interaction potential for He+H$_2$, we reveal how a combination of two shape resonances arising from $l=1$ and $l=2$ partial waves controls the stereodynamic outcome rather than a single $l=2$ partial wave attributed in the experiment. Further, for collision energies below 0.5 cm$^{-1}$, it is shown that stereodynamic preference for integral cross section follows a simple universal trend., Comment: 6 pages, 4 figures and 35 references and Supplementary Material (10 pages, 8 figures)

In this paper, we describe in detail an assembled open-path optical cavity to act as a temperature sensor of air. A metal absorption cell in a temperature-regulated tube furnace is placed at the center of an optical cavity. The optical cavity consists of two mirrors, two nitrogen buffer sleeves, and the open cell. The air is injected through a fitting in one extreme of the metal tube and travels half the tube length through a channel in the wall of the tube. The channel directs the air towards the center of the cell. The air flowing is heated at the temperature of the metal tube in contact with the furnace. The heated air injected at the center of the tube, flows towards the open extremes of the tube. The nitrogen buffer sleeves protect the mirrors from the heated air. The temperature of the air flowing through the tube is determined by measuring the absorption of the A band of oxygen as a function of the wavenumber in the 769–755 nm wavelength range. The absorption technique is phase-shift cavity ring down spectroscopy. To obtain the temperature, the energy of the lower rotational state for eleven selected rotational transitions is linearly fitted to a logarithmic function that contains the relative intensity of the rotational transition, the initial and final rotational quantum numbers and the energy of the transition. Accuracy of the measurement is determined by comparing the calculated temperature from the spectra with the analog reading of the temperature-regulated tube furnace. This technique is proposed for exhaust air temperature measurements of combustion chambers and cooling air after passing through the blades of a turbine.

We introduce a phenomenological model for a pairwise repulsive interaction potential of vortices in a type-II superconductor, consisting of superimposed sixfold and twelvefold anisotropies. Using numerical simulations we study how the vortex lattice configuration varies as the magnitudes of the two anisotropic interaction terms change. A triangular lattice appears for all values, and rotates through ${30}^{\ensuremath{\circ}}$ as the ratio of the sixfold and twlevefold anisotropy amplitudes is varied, in agreement with experimental results. The transition causes the vortex lattice to split into domains that have rotated clockwise or counterclockwise, with grain boundaries that are ``decorated'' by dislocations consisting of fivefold and sevenfold coordinated vortices. We also find intradomain dislocations and defects, and characterize them in terms of their energy cost. We discuss how this model could be generalized to other particle-based systems with anisotropic interactions, such as colloids, and consider the limit of very large anisotropy where it is possible to create cluster crystal states.

We investigate the potential for sensitively detecting millimeter-wave absorption through multiphoton ionization using the lowest rotational transition in CO (X1Σ, J = 1 ← J = 0) at 115 GHz as a diagnostic tool. This transition represents an almost perfect realization of a quantum mechanical two-level system. In the experiment, the output of a powerful continuous millimeter-wave source with sub-kilohertz resolution propagates counter to a pulsed molecular beam, causing Doppler shifted resonances. Absorption is detected by monitoring the involved rotational levels through resonance enhanced multiphoton ionization (REMPI). Observed polarization, saturation and Doppler effects demonstrate that the interaction with the millimeter-wave field is coherent and can be simulated well using the results for the two-level system. The combination of these results indicates that the millimeter-wave field is approximated well by a Gaussian beam with beam waist around 15 mm and constant effective electric field amplitude on the molecular beam axis. Time-correlated frequency modulation in the form of a short rectangular pulse is used to follow the molecular trajectory from the source to the laser interaction region. The experiments clearly demonstrate a great potential of extending high-resolution molecular beam spectroscopy with mass specific REMPI detection into the sub-terahertz or terahertz regimes.

The molecular ion D 2 H + is an important species in cold interstellar environments and a key benchmark for ab initio calculations. We have measured 37 transitions in the ν 1 fundamental band using the sub-Doppler technique Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy. Using an optical frequency comb for accurate frequency calibration, the uncertainties for most transitions were improved by more than an order of magnitude. These new measurements lead to improved predictions of pure rotational transition frequencies which have not been observed by THz observatories or laboratory spectrometers.

By applying various action spectroscopic techniques in a 4 K cryogenic ion trap instrument, protonated methanimine, CH2NH2+, has been investigated by high-resolution rovibrational and pure rotational spectroscopy for the first time. In total, 39 rovibrational transitions within the fundamental band of the ν2 symmetric C-H stretch were measured around 3026 cm-1, which were used to predict pure rotational transition frequencies of CH2NH2+ in the ground vibrational state. Based on these predictions, nine rotational transitions were observed between 109 and 283 GHz using a novel double resonance method, which significantly improved the sensitivity of the rotational measurements. This double resonance method consists of rotational excitation followed by vibrational excitation, which is finally detected as a dip in the number of CH2NH2+-He complexes formed in the 4 K He bath of the trap. The new measurements and the derived predictions of pure rotational transitions will enable the first radio-astronomical search for CH2NH2+.

The simultaneous monitoring of three stable isotopes of hydrogen sulphide (H2S), i.e. H232S, H233S, and H234S, within a single laser scan of 0.4 cm−1 has been achieved by means of a continuous-wave (cw) external-cavity quantum cascade laser (EC-QCL) coupled to high-resolution cavity ring-down spectroscopy (CRDS) near 7.5 μm. The measurement precisions of S32, S33, and S34 isotopes of H2S were found to be 1190 ppb, 13 ppb, and 124 ppb for the integration times of 264 s, 261 s, and 247 s, respectively. The mode-hop-free (MHF) tunability (1257 cm−1 to 1340 cm−1) of the EC-QCL was subsequently exploited to identify the interference-free 9 transition lines of H232S and H233S arising from the fundamental bending vibration (ν2) for the trace detection of H2S isotopes. A limiting sensitivity (1σ) of 20 ppb of total H2S concentration was achieved for an integration time of 250 s by targeting the rotational transition [i.e.] of (4, 4, 1) → (5, 5, 0), centred at ∼1292.857 cm−1. Finally, simultaneous monitoring of multiple trace species such as CH4, N2O, and H2S in a single laser scan of 0.05 cm−1 was demonstrated with high sensitivity and molecular specificity. The present study may lead to several potential future applications ranging from understanding of sulphur isotope geochemistry and fractionations to environmental sensing.

New ab initio potential energy surfaces have been generated for the ground state and low-lying excited states of the H+ + C3 system using the multireference configuration interaction (MRCI) method with Dunning’s augmented correlation consistent polarized valence quadruple-zeta (aug-cc-pVQZ) basis sets. The ground state and low-lying excited states show avoided crossing, indicating nonadiabatic coupling. The anisotropy of the ground-state surface has been analyzed by computing the multipolar expansion coefficients with the frozen C–C equilibrium bond length. The asymptotic potential has been merged with the interaction potential by spline fit. This potential is then used in the full close coupling calculations of rotational excitation in C3 collision with the proton for rotational levels j = 0, 2, 4, 6, 8 at very low collision energy. By averaging the cross sections over a Boltzmann distribution of velocities of the incoming atom, we obtain and discuss corresponding rate coefficients of C3 collision with t...

We present mass-correlated rotational alignment spectroscopy, based on the optical excitation of a coherent rotational quantum wave and the observation of temporal wave interferences in a mass spectrometer. Combined electronic and opto-mechanical delays increased the observation time and energy resolution by an order of magnitude compared with preceding time-domain measurements. Rotational transition frequencies were referenced to an external clock for accurate absolute frequency measurements. Rotational Raman spectra for six naturally occurring carbon disulfide isotopologues were resolved with 3 MHz resolution over a spectral range of 500 GHz. Rotational constants were determined with single-kilohertz accuracy, competitive with state-of-the-art frequency domain measurements.

The dependence of the spectral power of radiation in the transmission window of air near wavelength 2 mm on the altitude of stratospheric nuclear explosions is investigated. One of the rotational transition lines of nitrogen oxide NO is studied. Calculations of the time dependence of the nitrogen oxide concentration were performed by the method of mathematical modeling of plasma. It is shown that a large amount of nitrogen oxide is formed by explosion γ-rays in the partial-ionization region ahead of the shock wave front; the nitrogen oxide concentration reaches a quasistationary level and remains almost constant for hundreds of microseconds. The quasistationariness is maintained by secondary γ-rays arising in inelastic scattering of explosion neutrons. Estimates of the spectral power of radiation near wavelength 2 mm are obtained. It is shown that at altitude 45 km above the ground the spectral power of the radiation is 105 times greater than for ground-level explosions.

The resonance crossing of rotational levels with different fine-structure components and different k rotational quantum numbers was observed in the rotational spectra of the symmetric top fluorosulfate radical FSO3 . Detailed measurements were performed to analyze these weak resonances as well as the A1–A2 splittings of the K = 3 and K = 6 transitions. The resonance level crossing enabled the experimental determination of “forbidden” parameters, the rotational A and the centrifugal distortion DK constants as well as the corresponding resonance off-diagonal matrix element.

The rotational state of Envisat is re-estimated using the specular glint times in optical observation data obtained from 2013 to 2015. The model is simplified to a uniaxial symmetric model with the first order variation of its angular momentum subject to a gravity-gradient torque causing precession around the normal of the orbital plane. The sense of Envisat’s rotation can be derived from observational data, and is found to be opposite to the sense of its orbital motion. The rotational period is estimated to be ( 120.674 ± 0.068 ) · exp ( 4.5095 ± 0.0096 ) × 10 - 4 · t s , where t is measured in days from the beginning of 2013. The standard deviation is 0.760 s, making this the best fit obtained for Envisat in the literature to date. The results demonstrate that the angle between the angular momentum vector and the negative normal of the orbital plane librates around a mean value of 8.53 ° ± 0.42 ° with an amplitude from about 0.7 ° (in 2013) to 0.5 ° (in 2015), with the libration period equal to the precession period of the angular momentum, from about 4.8 days (in 2013) to 3.4 days (in 2015). The ratio of the minimum to maximum principal moments of inertia is estimated to be 0.0818 ± 0.0011 , and the initial longitude of the angular momentum in the orbital coordinate system is 40.5 ° ± 9.3 ° . The direction of the rotation axis derived from our results at September 23, 2013, UTC 20:57 is similar to the results obtained from satellite laser ranging data but about 20 ° closer to the negative normal of the orbital plane.

The harpooning model is firstly evidenced by the maximum impact parameter derived from AlO(Nmax) products with speed v′ ≈ 0 from the Al + O2 reaction., The harpooning mechanism has long been proposed for elementary reaction dynamics involving metals. It is characterized by an initial electron transfer (ET) process from the metal to the oxidant molecule. For the titled reaction Al + O2, the ET distance can be predicted to be 2.6 Å by simply calculating the energy difference between the ionization energy of the Al atom and the electron affinity of the O2 molecule. Hereby we experimentally derived the maximum impact parameter bmax of 2.5 ± 0.2 Å for the titled reaction, in consistency with the predicted ET distance. This derivation of bmax was achieved by using the crossed molecular beam experiment at a collision energy of 507 cm–1 (i.e. 1.45 kcal mol–1) with a high resolution time-sliced ion velocity imaging detection of the state-selective AlO products based on the (1 + 1) resonance-enhanced multiphoton ionization. The small rotational constant of the AlO(X2Σ+) radical (Be = 0.6413 cm–1) facilitated the formation of the AlO(v = 0) products in high rotational levels up to the energetically limited state, Nmax = 52, with an almost zero velocity mapping. Hence, in this extreme angular momentum disposal case, the collisional orbital angular momentum l was nearly completely channeled into the product rotational angular momentum as a consequence of the conservations of energy and angular momentum, offering a reaction system that breaks the restriction of kinematically favored mass combination in order to obtain information on the impact parameters. The present study yields the first direct derivation of bmax from the maximum rotational level of products under the experimental condition with the recoil energy E′T ≈ 0. This, in turn, provides solid evidence in supporting the harpooning mechanism.

Angewandte Chemie / International edition 56(41), 12512 – 12517 (2017). doi:10.1002/anie.201704901, We report the experimental demonstration of coherent enantiomer-selective enrichment of chiral molecules by employing a novel microwave five-pulse scheme. Our results show that enantiomers can be selectively transferred to a rotational level of choice by applying sequences of resonant microwave pulses in a phase- and polarization-controlled manner. This is achieved by simultaneously exciting all three kinds of electric dipole-allowed rotational transitions and monitoring the effect on a fourth rotational transition of choice. Using molecular beams, we apply our method to two chiral terpenes and obtain a 6 % enantiomeric enrichment, which is one order of magnitude larger than that recently reported in a buffer-gas cell experiment. This approach establishes a robust scheme for controlled manipulation of enantiomers using tailored microwave fields and opens up new avenues for chiral purification and enrichment that can be used in a broad scope of analytical or spectroscopic applications., Published by Wiley-VCH, Weinheim

Molecular dynamics investigation is performed on rotational fields in an isolated nanosized metal crystal at a certain temperature. Such fields are shown to exist even without external mechanical action. We investigate how the temperature and size of nanostructures affect specific rotational energies of atom subsystems. Statistical processing of the numerical data is used to find the dependence of the specific rotational energy of atoms on the structure temperature and size.

This work explores, from a numerical perspective, the role of particle rotational inertia on the magnetization dynamics of ferrofluids. A robust numerical method is used for this purpose. The numerical research code is based on the use of a convergent long range dipolar interactions technique. These interactions are computed through a sophisticated Ewald summation procedure. The balance of linear and angular momentum is solved for N ensembles containing N particles each. Long range dipolar magnetic torques are solved in a periodic system of Lattices, spread in physical and reciprocal spaces to assure the convergence on the calculation of the suspension transport properties. A small effect of particle rotational inertia is considered. The system of equations of N particles distributed randomly in space is solved simultaneously for different parallel realizations in order to achieve a meaningful statistics of our many-body system. The results are focused on the behavior of the suspension magnetization for different particle concentrations and intensities of rotational inertia. The physical parameter used to express this effect is the particle rotational Stokes number. The simulations indicate that, from a numerical perspective, rotational inertia may induce a relevant, but often neglected, effect on the magnetization equilibrium of a ferrofluid. This finding is relevant for the community of numericists interested in using Langevin Dynamics applied to dipolar suspensions. We propose an expression with a correction on the effect of the particle rotational inertia to compute the magnetization of a magnetic fluid. The results obtained in this work are compatible with some insights previously pointed out in former scientifical works.

The motion equations of diatomic molecules are here extended from the absolute vibrational case to a more general and real rotational and vibrational (rovibrational) case. The rovibrational Hamiltonian is heuristically formed by substituting the respective number and angular momentum operators for the vibrational and rotational quantum numbers in the energy eigenvalues of a diatomic molecule which was first introduced by Dunham. The motion equations of observable quantities such as the position and linear momentum are then determined by implementing the well-known Heisenberg relation in quantum mechanics. We face with the second-order imaginary differential equations for describing the temporal variations of the relative position and the linear momentum of two oscillating atoms, which are coupled in the x–y horizontal plane. The possible rovibrational oscillations are distinguished by the three quantum numbers n, l and m associated with the energy and angular momentum quantities. It is finally dem...

The frequencies and intensities of vibration–rotational transitions of water molecules in an argon matrix were calculated for temperatures of 6 and 30 K. The rigid asymmetric top approximation was used with available literature values of the effective rotational constants in the ground and excited vibrational states. The calculations were carried out by taking into account the existence of a non-equilibrium population distribution between the rotational levels of ortho- and para-water isomers. It was assumed that the temperature relaxation of the population of rotational levels is independent of the ortho- and para-isomers. Comparison of the results of the theoretical calculations with experimental literature data shows good agreement for the majority of the rotational structure lines for symmetric and antisymmetric stretching vibrations both in the frequency values and in the values of the relative intensities.

Future ultra-broadband and low-latency radio access networks pose stringent specifications for time synchronizations. For 5G base stations, inter-site timing error should be $ 1k) [3]. Recently, molecular clock referenced to sub-THz rotational transitions of carbonyl sulfide (OCS) gas emerged as a fully electronic solution with high stability [5]. In particular, chip-scale molecular clock (CSMC), built using a CMOS chip coupled with a waveguide OCS molecular cell, appeared as highly attractive for miniaturization and significant cost reduction. In [5], the long-term stability (3.8×10-10@averaging time $\tau=10^{ 3}\mathrm{S}$ ) of the CSMC was limited by the non-ideal measured OCS transition curve, which is susceptible to environmental disturbance. This paper presents a 70mW CSMC chip design that enables high-order dispersion-curve locking and enhances the long-term stability by 9x. Additional testing results also reveal its advantages in temperature stability over OCXO/OCMO and magnetic sensitivity over CSAC, respectively.

We propose a coherent optical method for creating negative refractive index (NRI) for a gaseous ensemble of ground-state polar molecules possessing both permanent electric and magnetic moments. Exploiting the pure rotational transition between the two lowest rotational levels of the ground vibrational state one can generate two dressed states of mixed parity using a microwave laser. These dressed states are then used as the two lower states of a {\Lambda}-type three-level scheme using two infrared lasers to couple them to another ro-vibrational level in the ground-state manifold. One of the infrared lasers is used as a weak probe and the other as a control field with a fixed detuning. We take into account local-field effects on the dielectric response of the medium at the probe frequency in terms of Clausius-Mossoti relation. We extract magnetic response out of purely dielectric response and calculate the magnetic permeability of the medium in terms of dielectric susceptibility. Our results show that there is a small frequency window near the two-photon resonance where both electric permittivity and magnetic permeability are negative with vanishingly small absorption. The figure of merit for the medium is shown to exceed unity. We interpret our results in terms of the proximity of EIT and quantum interference. We discuss the possible realization of our method using cold polar molecules that are recently experimentally produced., Comment: 16 pages, 4 figures. Version-2 is substantially modified following referees comments

Effect of external longitudinal magnetic field on the optical Free Induction Decay (FID) from a free radical was observed for the first time. The experiments were performed on the rotational transition of hydroxyl radical OH (2Π3/2(J=1) ← 2Π3/2(J=0) at 83.8 cm-1) using the Terahertz Free Electron Laser. In contrast to the results of the experiments with a stable paramagnetic molecule NO, the observed effect of external magnetic field on the Free Induction Decay from hydroxyl radicals is more complicated. A longitudinal magnetic field leads to rotation of the polarization plane of the FID radiation, as well as to additional modulation of the signal intensity. The angle of rotation of the polarization plane is large, in agreement with the theoretical predictions. The observed FID kinetics in the time domain are in semi-quantitative agreement with the modeling. This observation opens an opportunity for selective detection by polarization discrimination of weak signals of short-lived reactive paramagnetic free radicals from overwhelming signals that originate from stable non-paramagnetic species.

The 193-nm photolysis of CH(2)CHCN illustrates the capability of chirped-pulse Fourier transform millimeter-wave spectroscopy to characterize transition states. We investigate the HCN, HNC photofragments in highly excited vibrational states using both frequency and intensity information. Measured relative intensities of J = 1–0 rotational transition lines yield vibrational-level population distributions (VPD). These VPDs encode the properties of the parent molecule transition state at which the fragment molecule was born. A Poisson distribution formalism, based on the generalized Franck–Condon principle, is proposed as a framework for extracting information about the transition-state structure from the observed VPD. We employ the isotopologue CH(2)CDCN to disentangle the unimolecular 3-center DCN elimination mechanism from other pathways to HCN. Our experimental results reveal a previously unknown transition state that we tentatively associate with the HCN eliminated via a secondary, bimolecular reaction.

In the weak-field limit in which microwave spectroscopy is typically carried out, an application of a single-frequency pulse that is resonant with a molecular transition will create a coherence between the pair of states involved in the rotational transition, producing a free-induction decay (FID) that, after Fourier transform, produces a molecular signal at that same resonance frequency. With the advent of chirped-pulse Fourier transform microwave methods, the high-powered amplifiers needed to produce broadband microwave spectra also open up other experiments that probe the molecular response in the high-field regime. This paper describes a series of experiments involving resonant frequency pulses interrogating jet-cooled molecules under conditions of sufficient power to Rabi oscillate the two-state system through many Rabi cycles. The Fourier-transformed FID shows coherent signal not only at the applied resonant frequency but also at a series of transitions initially connected to the original one by sharing an upper or lower level with it. As the duration of the single-frequency excitation is increased from 250 to 1500 ns, the number of observed off-resonant, but dipole-allowed, molecular coherences grow. The phenomenon is quite general, having been demonstrated in Z-phenylvinylnitrile, E-phenylvinylnitrile (E-PVN), benzonitrile, guaiacol, and 4-pentynenitrile. In E-PVN, the highest power/longest pulse duration, coherent signal is also present at energetically nearby but not directly connected transitions. Even in molecular samples containing more than one independent species, only transitions due to the single species responsible for the original resonant transition are present. We develop a time-dependent model of the molecular/photon system and use it in conjunction with the experiment to test possible sources of the phenomenon.

Filling the terahertz gap Compared with other wavelengths, coherent sources of electromagnetic radiation in the terahertz regime are relatively scarce. Despite a number of applications in security imaging, spectroscopy, and chemical analysis, it has been experimentally challenging to produce such light. Chevalier et al. demonstrate an approach involving the excitation of a molecular gas with a quantum cascade laser. They show that they can tune into a broad range of desired wavelengths by carefully selecting the required molecular transition. A compact platform—the size of a shoe box—and widely tunable source of coherent terahertz radiation should find immediate application across a number of fields. Science , this issue p. 856

Conjugation and hyperconjugation are closely related stereoelectronic effects that are usually discussed in a qualitative fashion. It is possible to make it more quantitative. The natural bond orbital method provides a means of estimating the energetic consequence. They may also be studied by a charge shift analysis. Rotational barriers are often appropriately discussed in terms of such effects where the rotational transition state has broken the interaction between donor and acceptor atoms or groups. A comparison of charge distribution between the ground state and the transition state will show how much charge transfer occurs and if any other atoms are involved. This has been studied for substituted vinyl methyl ethers, substituted N,N-dimethylvinylamines, p-substituted anilines, and some esters and amides. Linear relationships were found for the rotational barriers vs the charge shifts. For some compounds, the σ- and π-components of the charge were obtained and showed that competition for σ-charge can lead to changes in the π-charge. Cases where there cannot be charge transfer are also discussed.

Rotational spectra of methyl cyanide were recorded newly and were analyzed together with existing spectra to extend the global model of low-lying vibrational states and their interactions to υ 4 = 1 at 920 cm−1. The rotational spectra cover large portions of the 36–1439 GHz region and reach quantum numbers J and K of 79 and 16, respectively. Information on the K level structure of CH3CN is obtained from IR spectra. A spectrum of 2 ν 8 around 717 cm−1, analyzed in our previous study, covered also the ν 4 band. The assignments in this band cover 880–952 cm−1, attaining quantum numbers J and K of 61 and 13, respectively. The most important interaction of υ 4 = 1 appears to be with υ 8 = 3 , Δ K = 0 , Δ l = + 3 , a previously characterized anharmonic resonance. We report new analyses of interactions with Δ K = - 2 and Δ l = + 1 , with Δ K = - 4 and Δ l = - 1 , and with Δ K = - 6 and Δ l = - 3 ; these four types of interactions connect all l substates of υ 8 = 3 in energy to υ 4 = 1 . A known Δ K = - 2 , Δ l = + 1 interaction with υ 7 = 1 was also analyzed, and investigations of the Δ K = + 1 , Δ l = - 2 and Δ K = + 3 , Δ l = 0 resonances with υ 8 = 2 were improved, as were interactions between successive states with υ 8 ⩽ 3 , mainly through new υ 8 ⩽ 2 rotational data. A preliminary single state analysis of the υ 4 = υ 8 = 1 state was carried out based on rotational transition frequencies and on ν 4 + ν 8 - ν 8 hot band data. A considerable fraction of the K levels was reproduced within uncertainties in its entirety or in part, despite obvious widespread perturbations in υ 4 = υ 8 = 1 . In addition to the interstellar detection of rotational transitions of methyl cyanide from within all vibrational states up to υ 4 = 1 , we report the tentative detection of υ 4 = υ 8 = 1 toward the main hot molecular core of the protocluster Sagittarius B2(N) employing the Atacama Large Millimeter/submillimeter Array.

The intermolecular potential energy surfaces (PESs) of the ground electronic state for the Rg-BrCl (Rg = He, Ne, Ar, Kr, Xe) van der Waals complexes have been constructed by using the coupled-cluster method in combination with the augmented quadruple-zeta correlation-consistent basis sets supplemented with an additional set of bond functions. The features of the anisotropic PESs for these complexes are remarkably similar, which are characterized by three minima and two saddle points between them. The global minimum corresponds to a collinear Rg-Br-Cl configuration. Two local minima, correlate with an anti-linear Rg-Cl-Br geometry and a nearly T-shaped structure, can also be located on each PES. The quantum bound state calculations enable us to investigate intermolecular vibrational states and rotational energy levels of the complexes. The transition frequencies are predicted and are fitted to obtain their corresponding spectroscopic constants. In general, the periodic trends are observed for this complex family. Comparisons with available experimental data for the collinear isomer of Ar-BrCl demonstrate reliability of our theoretical predictions, and our results for the other two isomers of Ar-BrCl as well as for other members of the complex family are also anticipated to be trustable. Except for the collinear isomer of Ar-BrCl, the data presented in this paper would be beneficial to improve our knowledge for these experimentally unknown species.

The emission spectrum induced in ultra-dense deuterium D(0) by a 1064 nm pulsed YAG laser with 0.4 J pulses is strongly dependent on the amount of D(0) formed. With D 2 pressure below 10 −2 mbar at the D(0) generator and no D(0) layer on the metal surface, line spectra can be observed with numerous lines due to metal and gas atoms. When a D(0) layer exists on the generator surface, these lines disappear. A different pattern of emission lines and bands is then found. Several peaks are observed which agree well with the rotational transitions of rotating D-D pairs in D(0) from theory. The peak widths are approximately 20 cm −1 . A prominent peak at 760 nm corresponds to spin state s = 3 in D(0) from a rotational transition J = 1 → 0. This gives an experimental D-D distance in this state of 5.052 ± 0.003 pm that is only 0.25% larger than predicted by theory and calculations. The existence of these rotational lines strongly supports the cluster model of D(0) described previously. At a few hundred mbar pressure, a red-emitting apparently self-focused beam is formed by the laser beam. The expected Balmer lines are weak or absent.

When exciting a ferromagnetic film with a femtosecond optical laser pulse, then there is a partial demagnetization within a few hundred fs. This means that the angular momentum of the electronic system is transferred to the lattice. This transfer is calculated by describing the lattice degrees of freedom as spin-phonon eigenmodes which have a sharp angular momentum. Possible other lattice degrees of freedom are mentioned but not considered explicitly. For Ni and Fe the calculated amount of transfer of angular momentum to the spin-phonon eigenmodes is rather small.

Pure rotational spectra of PbI and InI are interpreted to yield a full analytic potential energy function for each molecule. Rotational spectra for PbI have been retrieved from literature sources to perform the analysis. Rotational transition frequencies for excited vibrational states of InI (0 v B v and D v values are used to generate a set of “synthetic” pure R ( 0 ) transitions for each vibrational level. These are then fitted to an “Expanded Morse Oscillator” (EMO) potential using the direct-potential-fit program, dPOTFIT . The well-depth parameter, D e , is fixed at a literature value, while values of the equilibrium distance r e and EMO exponent-coefficient expansion (potential-shape) parameters are determined from the fits. Comparison with potential functions determined after including older mid-IR and visible electronic transition data shows that our analysis of the pure microwave data alone yields potential energy functions that accurately predict (to better than 1%) the overtone vibrational energies far beyond the range spanned by the levels for which the microwave data is available.

The efficient photoluminescence (PL) emission of solvated fullerenes has attracted significant interest because of their potential applications. Uncovering the possible factors that govern the PL emission of solvated fullerenes thus becomes important for the purpose of application. Here, we report a high pressure study on a typical solvated fullerene, C70*mesitylene, using the diamond anvil cell technique with associated spectroscopic measurements. Our Raman and PL spectra show that there is a change in the pressure dependence for the normalized PL intensity in solvated samples during the rotational transition. It indicates that the rotational state of C70 is a critical factor which can influence the PL emission of solvated samples. The optical absorption (OA) spectra further suggest that the C70–C70 interactions in solvated samples compared with those in desolvated samples are hindered under pressure because of the intercalation of solvent, which makes the PL emission in solvated samples more sensitive to the change in C70 rotations under pressure. Copyright © 2016 John Wiley & Sons, Ltd.

Using an orbital angular momentum-based communication system to increase the channel capacity has recently attracted more and more attention. This article proposes a novel antenna array to transmit and receive orbital angular momentum beams at a radio frequency (3 GHz) by using delay in space. Different from the well-known uniform circular array which needs a phase-shifting network, every element in the proposed helicoidal array has the same phase. As long there are enough array elements and a power divider, arbitrary orbital angular momentum mode can be generated easily by only changing the positions of the array elements without any phase-shifting. In this experiment, l = 1 and l = 2 helicoidal arrays with eight half-wavelength dipoles are fabricated. The simulated and measured results, such as S parameters, near-field orbital angular momentum properties, far-field orbital angular momentum properties, the channel isolation between different orbital angular momentum channel, and the packet-loss-r...

We present numerical simulations of molecular clouds (MCs) with self-consistent CO gas-phase and isotope chemistry in various environments. The simulations are post-processed with a line radiative transfer code to obtain $^{12}$CO and $^{13}$CO emission maps for the $J=1\rightarrow0$ rotational transition. The emission maps are analysed with commonly used observational methods, i.e. the $^{13}$CO column density measurement, the virial mass estimate and the so-called $X_{\textrm{CO}}$ (also CO-to-H$_2$) conversion factor, and then the inferred quantities (i.e. mass and column density) are compared to the physical values. We generally find that most methods examined here recover the CO-emitting H$_{2}$ gas mass of MCs within a factor of two uncertainty if the metallicity is not too low. The exception is the $^{13}$CO column density method. It is affected by chemical and optical depth issues, and it measures both the true H$_{2}$ column density distribution and the molecular mass poorly. The virial mass estimate seems to work the best in the considered metallicity and radiation field strength range, even when the overall virial parameter of the cloud is above the equilibrium value. This is explained by a systematically lower virial parameter (i.e. closer to equilibrium) in the CO-emitting regions; in CO emission, clouds might seem (sub-)virial, even when, in fact, they are expanding or being dispersed. A single CO-to-H$_{2}$ conversion factor appears to be a robust choice over relatively wide ranges of cloud conditions, unless the metallicity is low. The methods which try to take the metallicity dependence of the conversion factor into account tend to systematically overestimate the true cloud masses., Comment: 24 pages, 11 figures. This is a pre-copyedited, author-produced PDF of an article accepted for publication in MNRAS following peer review

Molecules with hyperfine splitting of their rotational line spectra are useful probes of optical depth, via the relative line strengths of their hyperfine components.The hyperfine splitting is particularly advantageous in interpreting the physical conditions of the emitting gas because with a second rotational transition, both gas density and temperature can be derived. For HCN however, the relative strengths of the hyperfine lines are anomalous. They appear in ratios which can vary significantly from source to source, and are inconsistent with local thermodynamic equilibrium. This is the HCN hyperfine anomaly, and it prevents the use of simple LTE models of HCN emission to derive reliable optical depths. In this paper we demonstrate how to model HCN hyperfine line emission, and derive accurate line ratios, spectral line shapes and optical depths. We show that by carrying out radiative transfer calculations over each hyperfine level individually, as opposed to summing them over each rotational level, the anomalous hyperfine emission emerges naturally. To do this requires not only accurate radiative rates between hyperfine states, but also accurate collisional rates. We investigate the effects of different sets of hyperfine collisional rates, derived via the 'proportional method' and through direct recoupling calculations. Through an extensive parameter sweep over typical low mass star forming conditions, we show the HCN line ratios to be highly variable to optical depth. We also reproduce an observed effect whereby the red-blue asymmetry of the hyperfine lines (an infall signature) switches sense within a single rotational transition., Comment: 12 pages, 7 figures. Accepted for publication in MNRAS

The laser-induced fluorescence spectra of the jet-cooled ScO molecules have been investigated in the 27,400−28,000 cm−1 region at 0.04 cm−1 resolution. The D2Σ+state of ScO, predicted by the earlier ab initio studies, was observed in v = 0 vibration from the ground X2Σ+ state. The C2Πi state, earlier reported by us in vibrations v = 0 − 3, was also observed in v = 4 along with the A2Πr state in v = 14 vibration. The energetically overlapping v = 0 of the D2Σ+and v = 4 of the C2Πi states are perturbed by homogeneous spin-orbit, spin-electronic and J-dependent l -uncouple interactions. The rotational transition wavenumbers of the D2Σ+−X2Σ+(0,0) and C2Πi − X2Σ+(4,0) bands were fitted together using single Hamiltonian matrix that included 2Π and 2Σ+ matrix elements and their off-diagonal elements. The deperturbed D2Σ+, v = 0 state was found to be only 11.5 cm−1 below that of the C2Π3/2, v = 4 sub-state and f- and e-levels respectively cross after J = 12.5 and 28.5. The dispersed fluorescence and wavelength separated excitation spectra were crucial in understanding the spectra and the deperturbation analysis of these interacting vibronic states. The D2Σ+, v = 0 state showed J- and parity-dependent mixing up to ~45% by the C2Πi, v = 4 state and is reflected in the disperse fluorescence spectra. The radiative lifetimes of the A2Πr, C2Πi and D2Σ+ states respectively in 14, 4 and 0 vibrations also indicate that the C − D as well as A − C states interact. The observed sign and relative magnitude of the spin-rotation constant γ of the ground X2Σ+, and excited D2Σ+states are elucidated qualitatively in light of second-order contribution to γ from the A 2Πr and C 2Πi states.