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The propargyl cation, H2CCCH+, is a crucial hydrocarbon precursor in the chemical evolution of the interstellar medium (ISM). It serves as a key intermediate for understanding ISM hydrocarbon chemistry. This work presents state-to-state collisional rate coefficients for rotational excitation and de-excitation of ortho- and para- H2CCCH+ colliding with He at ISM-relevant temperatures (T  ≤ 60 K). We employed a high-level post-Hartree-Fock CCSD(T)-F12/aug-cc-pVTZ method to generate a 3D interaction potential energy surface (3D-PES) for the weakly bound H2CCCH+-He complex. The analytical 3D-PES was then used in close-coupling calculations to determine cross-sections for rotational excitation and de-excitation of ortho- and para- H2CCCH+ by collisions with He for kinetic energies (Ek) up to 300 cm−1. Inelastic collision rate coefficients were subsequently obtained by thermally averaging the cross-sections over a Maxwell–Boltzmann distribution of kinetic energies. Our results indicate that at very low temperatures (T  < 15 K), rotational transitions associated with Δj = Δkc = ±1, which are crucial for the identification of H2CCCH+ in astronomical surveys, exhibit the largest cross-sections. In contrast, at higher temperatures, transitions with Δj = Δkc = ±2 become more dominant. These data hold significant implications for the determination of the H2CCCH+ abundance in the ISM and improve the modelling of interstellar hydrocarbon-chain reaction pathways. [ABSTRACT FROM AUTHOR]

State-to-state cross sections and rate coefficients for transitions between rotational/fine-structure levels of OH(X2Π) induced by collisions with atomic hydrogen are reported in this work. The scattering calculations take into account the full open-shell character of the OH + H system and include the four potential energy surfaces (1A′, 1A″, 3A′, 3A″) that correlate with the OH(X2Π) + H(2S) asymptote. Three of these surfaces are repulsive, while the deep H2O well is present on one surface (1A′). The OH + H potential energy curves calculated by Alexander et al. [J. Chem. Phys. 121, 5221 (2004)] are employed in this work. Time independent quantum scattering calculations were performed using the quantum statistical method of Rackham and co-workers [Chem. Phys. Lett. 343, 356 (2001)] because of the presence of the deep H2O well. The computed cross sections include contributions from direct scattering, as well formation and decay of a transient collision complex since the transient HO–H complex is expected to decay nonreactively. Rate coefficients for OH–H inelastic collisions are of interest for astrophysical applications. [ABSTRACT FROM AUTHOR]

We present a joint experimental and theoretical study of rotationally inelastic collisions between NO (X2Π1/2, ν = 0, j = 1/2, f) radicals and CO (X1Σ+, ν = 0, j = 0) molecules at a collision energy of 220 cm−1. State-to-state scattering images for excitation of NO radicals into various final states were measured with high resolution by combining the Stark deceleration and velocity map imaging techniques. The high image resolution afforded the observation of correlated rotational excitations of NO–CO pairs, which revealed a number of striking scattering phenomena. The so-called "parity-pair" transitions in NO are found to have similar differential cross sections, independent of the concurrent excitation of CO, extending this well-known effect for collisions between NO and rare gas atoms into the realm of bimolecular collisions. Forward scattering is found for collisions that induce a large amount of rotational energy transfer (in either NO, CO, or both), which require low impact parameters to induce sufficient energy transfer. This observation is interpreted in terms of the recently discovered hard collision glory scattering mechanism, which predicts the forward bending of initially backward receding trajectories if the energy uptake in the collision is substantial in relation to the collision energy. The experimental results are in good agreement with the predictions from coupled-channels quantum scattering calculations based on an ab initio NO–CO potential energy surface. [ABSTRACT FROM AUTHOR]

Inelastic collisions and elementary chemical reactions proceeding through the formation and subsequent decay of an intermediate collision complex, with an associated deep well on the potential energy surface, pose a challenge for accurate fully quantum mechanical approaches, such as the close-coupling method. In this study, we report on the theoretical prediction of temperature-dependent state-to-state rate coefficients for these complex-mode processes, using a statistical quantum method. This statistical adiabatic channel model is benchmarked by a direct comparison using accurate rate coefficients from the literature for a number of systems (H2 + H+, HD + H+, SH+ + H, and CH+ + H) of interest in astrochemistry and astrophysics. For all of the systems considered, an error of less than factor 2 was found, at least for the dominant transitions and at low temperatures, which is sufficiently accurate for applications in the above mentioned disciplines. [ABSTRACT FROM AUTHOR]

Modeling protoplanetary disks and other interstellar media that are not in local thermal equilibrium require the knowledge of rovibrational transition rate coefficients of molecules in collision with helium and hydrogen. We present a computational method based on the numerically exact coupled-channel (CC) method for rotational transitions and a multi-channel distorted-wave Born approximation (MC-DWBA) for vibrational transitions to calculate state-to-state rate coefficients. We apply this method to the astrophysically important case of CO2–He collisions, using newly computed ab initio three-dimensional potential energy surfaces for CO2–He with CO2 distorted along the symmetric and asymmetric stretch (ν1 and ν3) coordinates. It is shown that the MC-DWBA method is almost as accurate as full CC calculations, but more efficient. We also made computations with the more approximate vibrational coupled-channel rotational infinite-order sudden method but found that this method strongly underestimates the vibrationally inelastic collision cross sections and rate coefficients for both CO2 modes considered. [ABSTRACT FROM AUTHOR]

The anion C5N− is one of the largest linear (C,N)-bearing chains detected in the interstellar medium. Here we present and discuss the general features of new ab initio potential energy surfaces describing the interaction of this linear anion with He and H2. We employ a Legendre Polynomials expansion representation for the former and an artificial neural network fit for the latter. We then carry out quantum scattering calculations to yield rotationally inelastic cross-sections for collisions with He and H2, using relative translational energy values in the range of 0.1–300 cm−1. We then obtained the corresponding inelastic rate coefficients as a function of temperature covering the range from 1 to 100 K. The results for these two systems are compared with each other, as well as with the earlier results on the C3N− colliding with the same partners. We found that the final inelastic rate coefficients for this anion are all fairly large, those from collisions with H2 being the largest. The consequences of such findings on their non-equilibrium rotational populations in interstellar environments are discussed in our conclusions. [ABSTRACT FROM AUTHOR]

The anion C5N− is one of the largest linear (C,N)-bearing chains detected in the interstellar medium. Here we present and discuss the general features of new ab initio potential energy surfaces describing the interaction of this linear anion with He and H2. We employ a Legendre Polynomials expansion representation for the former and an artificial neural network fit for the latter. We then carry out quantum scattering calculations to yield rotationally inelastic cross-sections for collisions with He and H2, using relative translational energy values in the range of 0.1–300 cm−1. We then obtained the corresponding inelastic rate coefficients as a function of temperature covering the range from 1 to 100 K. The results for these two systems are compared with each other, as well as with the earlier results on the C3N− colliding with the same partners. We found that the final inelastic rate coefficients for this anion are all fairly large, those from collisions with H2 being the largest. The consequences of such findings on their non-equilibrium rotational populations in interstellar environments are discussed in our conclusions. [ABSTRACT FROM AUTHOR]

Rate coefficients for vibrational energy transfer are calculated for collisions between molecular nitrogen and hydrogen in a wide range of temperature and of initial vibrational states ( v ≤ 40 for N 2 and w ≤ 10 for H 2 ). These data are needed for the modelling of discharges in N 2 /H 2 plasma or of atmospheric and interstellar medium chemistry in different temperature ranges. The calculations were performed by a mixed quantum-classical method, to recover quantum effects associated with the vibrational motion, on a refined potential energy surface. The obtained rates present striking discrepancies with those evaluated by first-order perturbation theories, like the SSH (Schwartz, Slavsky, Herzfeld) theory, which are often adopted in kinetic modelling. In addition, we present a detailed, though preliminary, analysis on the performance of different Machine Learning models based on the Gaussian Process or Neural Network techniques to produce complete datasets of inelastic scattering rate coefficients. Eventually, by using the selected models, we give the complete dataset (i.e., covering the whole vibrational ladder) of rate coefficients for the N 2 (v) + H 2 (0) ⟶ N 2 (v - Δ v) + H 2 (0) , Δ v = 1 , 2 , 3 processes. [ABSTRACT FROM AUTHOR]

We examine rotational transitions of HCl in collisions with H2 by carrying out quantum mechanical close-coupling and quasi-classical trajectory (QCT) calculations on a recently developed globally accurate full-dimensional ab initio potential energy surface for the H3Cl 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 the classification of rainbow scattering into rotational and l-type rainbows is effective for H2 + HCl collisions. While the QCT 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. [ABSTRACT FROM AUTHOR]

The vibrational quenching cross sections and corresponding low-temperature rate constants for the ν = 1 and ν = 2 states of CN−(1Σ+) colliding with He and Ar atoms have been computed ab initio using new three-dimensional potential energy surfaces. Little work has been carried out so far on low-energy vibrationally inelastic collisions for anions with neutral atoms. The cross sections and rates calculated at energies and temperatures relevant for both ion traps and astrochemical modeling are found by the present calculations to be even smaller than those of the similar C 2 − /He and C 2 − /Ar systems, which are in turn of the order of those existing for the collisions involving neutral diatom–atom systems. The implications of our finding in the present case mainly focus on the possible role of small computed rate constants in the dynamics of molecular cooling and the evolution of astrochemical modeling networks. [ABSTRACT FROM AUTHOR]

A new spin-averaged potential energy surface (PES) for non-reactive O2( Σ g − 3 ) + O2( Σ g − 3 ) collisions is presented. The potential is formulated analytically according to the nature of the principal interaction components, with the main van der Waals contribution described through the improved Lennard-Jones model. All the parameters involved in the formulation, having a physical meaning, have been modulated in restricted variation ranges, exploiting a combined analysis of experimental and ab initio reference data. The new PES is shown to be able to reproduce a wealth of different physical properties, ranging from the second virial coefficients to transport properties (shear viscosity and thermal conductivity) and rate coefficients for inelastic scattering collisions. Rate coefficients for the vibrational inelastic processes of O2, including both vibration-to-vibration (V–V) and vibration-to-translation/rotation (V–T/R) energy exchanges, were then calculated on this PES using a mixed quantum–classical method. The effective formulation of the potential and its combination with an efficient, yet accurate, nuclear dynamics treatment allowed for the determination of a large database of V–V and V–T/R energy transfer rate coefficients in a wide temperature range. [ABSTRACT FROM AUTHOR]

Two different ab initio potential energy surfaces are employed to investigate the efficiency of the rotational excitation channels for the polar molecular ion HeH+ interacting with He atoms. We further use them to investigate the quantum dynamics of both the proton-exchange reaction and the purely rotational inelastic collisions over a broad range of temperatures. In current modeling studies, this cation is considered to be one of the possible cooling sources under early universe conditions after the recombination era and has recently been found to exist in the interstellar medium. The results from the present calculations are able to show the large efficiency of the state-changing channels involving rotational states of this cation. In fact, we find them to be similar in size and behavior to the inelastic and reaction rate coefficients obtained in previous studies, where H atoms were employed as projectiles. The same rotational excitation processes, occurring when free electrons are the collision partners of this cation, are also compared with the present findings. The relative importance of the reactive, proton-exchange channel and the purely inelastic channels is also analyzed and discussed. The rotational de-excitation processes are also investigated for the cooling kinetics of the present cation under cold trap conditions with He as the buffer gas. The implications of the present results for setting up more comprehensive numerical models to describe the chemical evolution networks in different environments are briefly discussed. [ABSTRACT FROM AUTHOR]

The experimental characterization of scattering resonances in low energy collisions has proven to be a stringent test for quantum chemistry calculations. Previous measurements on the NO–H2 system at energies down to 10 cm−1 challenged the most sophisticated calculations of potential energy surfaces available. In this report, we continue these investigations by measuring the scattering behavior of the NO–H2 system in the previously unexplored 0.4 cm−1–10 cm−1 region for the parity changing de-excitation channel of NO. We study state-specific inelastic collisions with both para- and ortho-H2 in a crossed molecular beam experiment involving Stark deceleration and velocity map imaging. We are able to resolve resonance features in the measured integral and differential cross sections. Results are compared to predictions from two previously available potential energy surfaces, and we are able to clearly discriminate between the two potentials. We furthermore identify the partial wave contributions to these resonances and investigate the nature of the differences between collisions with para- and ortho-H2. Additionally, we tune the energy spreads in the experiment to our advantage to probe scattering behavior at energies beyond our mean experimental limit. [ABSTRACT FROM AUTHOR]

We present quasiclassical trajectory simulations of O2 + O collisions under conditions representative of a crossed molecular beam experiment [Lahankar et al., J. Phys. Chem. A 120, 5348–5359 (2016)]. These calculations are compared to experimental data in order to further validate Potential Energy Surfaces (PESs) recently developed at the University of Minnesota [Z. Varga, Y. Paukku, and D. G. Truhlar, J. Chem. Phys. 147, 154312 (2017)]. Spin and spatial symmetries allow nine adiabatic PESs to represent the ground state interactions of O2 + O. We simulate trajectories adiabatically on all nine surfaces and perform analysis on data from each surface separately and the combined set of nine. It is shown that aggregated adiabatic calculations from nine surfaces agree better with the experiment for both inelastic and exchange collisions than a previous study that used a single surface and lie within the reported experimental uncertainty at almost all points. Distributions for exchange reactions using all nine PESs are interpreted using each surface's opacity function and activation energy for exchange. Rovibrationally resolved product distributions are then studied for a better understanding of energy relaxation in exchange collisions and may prove useful for further quasiclassical trajectory study and new experiments that use rovibrational spectroscopy to resolve the internal energy of the scattered products. [ABSTRACT FROM AUTHOR]

We present a combined experimental and theoretical study of state-to-state inelastic collisions between NO (X2Π1/2, j = 1/2, f) radicals and D2 (j = 0, 1, 2, 3) molecules at collision energies of 100 cm−1 and 750 cm−1. Using the combination of Stark deceleration and velocity map imaging, we fully resolve pair-correlated excitations in the scattered molecules. Both spin–orbit conserving and spin–orbit changing transitions in the NO radical are measured, while the coincident rotational excitation (j = 0 → j = 2) and rotational de-excitation (j = 2 → j = 0 and j = 3 → j = 1) in D2 are observed. De-excitation of D2 shows a strong dependence on the spin–orbit excitation of NO. We observe translation-to-rotation energy transfer as well as direct rotation-to-rotation energy transfer at the lowest collision energy probed. The experimental results are in good agreement with cross sections obtained from quantum coupled-channels calculations based on recent NO–D2 potential energy surfaces. The observed trends in the correlated scattering cross sections are understood in terms of the NO–D2 quadrupole–quadrupole interaction. [ABSTRACT FROM AUTHOR]

We present a MultiConfiguration Time Dependent Hartree (MCTDH) method as an attractive alternative approach to the usual quantum close-coupling method that approaches some computational limits in the calculation of rotational excitation (and de-excitation) between polyatomic molecules (here collisions between triatomic and diatomic rigid molecules). We have performed a computational investigation of the rotational (de-)excitation of the benchmark rigid rotor H2O–H2 system on a recently developed Potential Energy Surface of the complex using the MCTDH method. We focus here on excitations and de-excitations from the 000, 111, and 110 states of H2O with H2 in its ground rotational state, looking at all the potential transitions in the energy range 1–200 cm−1. This work follows a recently completed study on the H2O–H2 cluster where we characterized its spectroscopy and more generally serves a broader goal to describe inelastic collision processes of high dimensional systems using the MCTDH method. We find that the cross sections obtained from the MCTDH calculations are in excellent agreement with time independent calculations from previous studies but does become challenging for the lower kinetic energy range of the de-excitation process: that is, below approximately 20 cm−1 of collision energy, calculations with a relative modest basis become unreliable. The MCTDH method therefore appears to be a useful complement to standard approaches to study inelastic collision for various collision partners, even at low energy, though performing better for rotational excitation than for de-excitation. [ABSTRACT FROM AUTHOR]

HCS+ ions have been detected in several regions of the interstellar medium (ISM), but an accurate determination of the chemical-physical conditions in the molecular clouds where this molecule is observed requires detailed knowledge of the collisional rate coefficients with the most common colliders in those environments. In this work, we study the dynamics of rotationally inelastic collisions of HCS+ + H2 at low temperature, and report, for the first time, a set of rate coefficients for this system. We used a recently developed potential energy surface for the HCS+–H2 van der Waals complex and computed state-to-state rotational rate coefficients for the lower rotational states of HCS+ in collision with both para - and ortho -H2, analysing the influence of the computed rate coefficients on the determination of critical densities. Additionally, the computed rate coefficients are compared with those obtained by scaling the ones from HCS+ in collision with He (an approximation that is sometimes used when data is lacking), and large differences are found. Furthermore, the approximation of using the rates for the HCO+ + H2 collision as a rough approximation for those of the HCS+ + H2 system is also evaluated. Finally, the complete set of de-excitation rate coefficients for the lowest 30 rotational states of HCS+ by collision with H2 is reported from 5 to 100 K. [ABSTRACT FROM AUTHOR]

Building on our previous work on NO + Ar, this paper presents a complete set of orientation measurements and quantum mechanical calculations for the NO + Kr collision system, including both spin-orbit conserving and changing collisions, and both side-on (x-axis) and end-on (z-axis) orientations. While many of the trends observed in the oriented differential and integral scattering distributions, as well as in the spin-orbit branching fractions, are similar to the ones seen previously for NO + Ar, a direct comparison with the Ar data reveals subtle differences in the scattering dynamics, which we rationalise with the more extended attractive regions on the NO + Kr potential energy surfaces. High-impact parameter collisions that lead to low scattering angles in the spin-orbit conserving manifold are particularly sensitive to the topology in the attractive parts of the potential, whereas more impulsive, low-impact parameter trajectories, which sample the repulsive parts of the potential, produce very similar features in the oriented differential cross sections for the Ar and Kr systems, especially for spin-orbit changing collisions. [ABSTRACT FROM AUTHOR]

The potential energy surface describing the interaction of methylene (CH 2 ) in its ground X ~ 3 B 1 electronic state with molecular hydrogen has been calculated through explicitly correlated coupled cluster theory with inclusion of single, double, and (perturbatively) triple excitations [RCCSD(T)-F12a] and a correlation-consistent aug-cc-pVTZ basis. The calculated points for various geometries of the CH 2 –H 2 complex were fit to a functional form suitable for use in time-independent quantum scattering calculations of cross sections for collision-induced transitions between CH 2 rotational levels. The well depth D e of the CH 2 –H 2 complex was found to equal 92.1 cm − 1 in a planar geometry and intermolecular separation R = 6.55 a 0 . A representative set of cross sections is presented and compared with cross sections for the corresponding transitions in methylene induced by collisions with helium. [ABSTRACT FROM AUTHOR]

The scattering cross-sections and corresponding rate coefficients for rotationally inelastic collisions of 12 C 2 − ( 2 Σ g + ) with H 2 ( 1 Σ g + ) are presented over a broad range of cold-trap temperatures. They have been calculated using quantum scattering theory that employs a new ab initio potential energy surface. The rate coefficients for the inelastic processes in the anionic partner are used to model the thermalisation dynamics of 12 C 2 − using H 2 as a buffer gas, a trap partner which is found here to be far more efficient than the typical buffer gas He and even more so than when using Ar as a partner gas. The microscopic physics underlying these findings is discussed in some detail. We additionally compute and discuss 12 C 2 − quadrupole transitions by spontaneous emission and use the newly computed rates to show that the anion's rotational levels should be in local thermal equilibrium at typical interstellar conditions. [ABSTRACT FROM AUTHOR]

We compute a new potential energy surface (PES) for the study of the inelastic collisions between N2H+ and H2 molecules. A preliminary study of the reactivity of N2H+ with H2 shows that neglecting reactive channels in collisional excitation studies is certainly valid at low temperatures. The four dimensional (4D) N2H+-H2 PES is obtained from electronic structure calculations using the coupled cluster with single, double, and perturbative triple excitation level of theory. The atoms are described by the augmented correlation consistent triple zeta basis set. Both molecules were treated as rigid rotors. The potential energy surface exhibits a well depth of 2530 cm-1. Considering this very deep well, it appears that converged scattering calculations that take into account the rotational structure of both N2H+ and H2 should be very difficult to carry out. To overcome this difficulty, the "adiabatic-hindered-rotor" treatment, which allows para-H2(j = 0) to be treated as if it were spherical, was used in order to reduce the scattering calculations to a 2D problem. The validity of this approach is checked and we find that cross sections and rate coefficients computed from the adiabatic reduced surface are in very good agreement with the full 4D calculations. [ABSTRACT FROM AUTHOR]

We compute a new potential energy surface (PES) for the study of the inelastic collisions between N2H+ and H2 molecules. A preliminary study of the reactivity of N2H+ with H2 shows that neglecting reactive channels in collisional excitation studies is certainly valid at low temperatures. The four dimensional (4D) N2H+-H2 PES is obtained from electronic structure calculations using the coupled cluster with single, double, and perturbative triple excitation level of theory. The atoms are described by the augmented correlation consistent triple zeta basis set. Both molecules were treated as rigid rotors. The potential energy surface exhibits a well depth of 2530 cm-1. Considering this very deep well, it appears that converged scattering calculations that take into account the rotational structure of both N2H+ and H2 should be very difficult to carry out. To overcome this difficulty, the "adiabatic-hindered-rotor" treatment, which allows para-H2(j = 0) to be treated as if it were spherical, was used in order to reduce the scattering calculations to a 2D problem. The validity of this approach is checked and we find that cross sections and rate coefficients computed from the adiabatic reduced surface are in very good agreement with the full 4D calculations. [ABSTRACT FROM AUTHOR]

We have performed extensive calculations to investigate thermal energy, rotationally inelastic collisions of NaK(A¹Σ+) with He. We determined a potential energy surface using a multi-reference configuration interaction wave function as implemented by the GAMESS electronic structure code, and we have performed coupled channel scattering calculations using the Arthurs and Dalgarno formalism. We also calculate the Grawert coefficients Bλ(j, j') for each j → j' transition. These coefficients are used to determine the probability that orientation and alignment are preserved in collisions taking place in a cell environment. The calculations include all rotational levels with j or j' between 0 and 50, and total (translational and rotational) energies in the range 0.0002-C0.0025 a.u. (~44-C550 cm-1). The calculated cross sections for transitions with even values of Δj tend to be larger than those for transitions with odd Δj, in agreement with the recent experiments of Wolfe et al. (J. Chem. Phys. 134, 174301 (2011)). The calculations of the energy dependence of the cross sections and the calculations of the fraction of orientation and alignment preserved in collisions also exhibit distinctly different behaviors for odd and even values of Δj. The calculations also indicate that the average fraction of orientation or alignment preserved in a transition becomes larger as j increases. We interpret this behavior using the semiclassical model of Derouard, which also leads to a simple way of visualizing the distribution of the angles between the initial and final angular momentum vectors j and j'. Finally, we compare the exact quantum results for j → j' transitions with results based on the simpler, energy sudden approximation. That approximation is shown to be quite accurate. [ABSTRACT FROM AUTHOR]

We present a new four-dimensional (4D) potential energy surface for the HCl-H2 van der Waals system. Both molecules were treated as rigid rotors. Potential energy surface was obtained from electronic structure calculations using a coupled cluster with single, double, and perturbative triple excitations method. The four atoms were described using the augmented correlation-consistent quadruple zeta basis set and bond functions were placed at mid-distance between the HCl and H2 centers of mass for a better description of the van der Waals interaction. The global minimum is characterized by the well depth of 213.38 cm-1 corresponding to the T-shape structure with H2 molecule on the H side of the HCl molecule. The dissociation energies D0 are 34.7 cm-1 and 42.3 cm-1 for the complex with para- and ortho-H2, respectively. These theoretical results obtained using our new PES are in good agreement with experimental values [D. T. Anderson, M. Schuder, and D. J. Nesbitt, Chem. Phys. 239, 253 (1998)]. Close coupling calculations of the inelastic integral rotational cross sections of HCl in collisions with para-H2 and ortho-H2 were performed at low and intermediate collisional energies. Significant differences exist between para- and ortho-H2 results. The strongest collision-induced rotational HCl transitions are the transitions with Δj = 1 for collisions with both para-H2 and ortho-H2. Rotational relaxation of HCl in collision with para-H2 in the rotationally excited states j = 2 is dominated by near-resonant energy transfer. [ABSTRACT FROM AUTHOR]

Quantum mechanical investigation of the rotationally inelastic collisions of CS with ortho- and para-H2 molecules is reported. The new global four-dimensional potential energy surface presented in our recent work is used. Close coupling scattering calculations are performed in the rigid rotor approximation for ortho- and para-H2 colliding with CS in the j = 0-15 rotational levels and for collision energies ranging from 10-2 to 103 cm-1. The cross sections and rate coefficients for selected rotational transitions of CS are compared with the ones previously reported for the collision of CS with He. The largest discrepancies are observed at low collision energy, below 1 cm-1. Above 10 cm-1, the approximation using the square root of the relative mass of the colliders to calculate the cross sections between a molecule and H2 from the data available with 4He is found to be a good qualitative approximation. The rate coefficients calculated with the electron gas model for the He-CS system show more discrepancy with our accurate results. However, scaling up these rates by a factor of 2 gives a qualitative agreement. [ABSTRACT FROM AUTHOR]

A newly calculated ab initio potential energy surface is used to compute collision-driven state-changing cross sections and rate coefficients over a range from 5 to 100 K for CN−(1Σ), the smallest anion detected in the interstellar medium, interacting with He, an abundant species in this environment. We compare our presently computed rate coefficients with those previously published for the similar and important systems CN–He, CN-H2, and CN−–H2 to illustrate the broader network of inelastic, state-changing processes for these four systems. We also discuss the size-scaling effects that occur when changing partners from He to H2. We further analyze the differences in size between collision-driven rate coefficients when going from neutral CN to its anion. All the present results are discussed in detail, to provide accurate and realistic data for chemical networks that wish to include the CN− anion in their modeling of astrochemical environments. [ABSTRACT FROM AUTHOR]

The cross sections and rate constants of pure rotational and ro-vibrational inelastic collision processes for the D2–HF system were investigated by employing the recently developed coupled-states approximation including the nearest neighbor Coriolis couplings, based on our newly constructed potential energy surface. The state-to-state cross sections and rate constants were found to follow the usual energy and angular momentum gap laws for pure rotational and ro-vibrational energy transfer processes. The calculated rate constant of 1.18 × 10-10 cm3 mol−1 s−1 for D2(v1=0) + HF(v2=0, j2=13) is very close to the experimental value of (1.2 ± 0.2) × 10-10 cm3 mol−1 s−1. The calculated vibrational-resolved rate constants are in reasonably consistent to the available experimental results and follow the similar trend with temperature. [ABSTRACT FROM AUTHOR]

In this research, we reported an interpolated potential energy surface (PES) from ab initio electronic energy of molecular fragments for NH + OH reaction and isotopic substitution. Classical trajectory simulations were performed on this surface to determine reaction probabilities and reaction cross sections in various channels. Also, reaction probability and reaction cross section as a function of the translation energy of fragments were shown. For inelastic collision, the conversion of kinetic energy of particles into internal energy or kinetic energy of another particle was studied. The effect of the impact parameter and relative translational energy of particles on the deflection angle was also investigated. Nonlinear least squares fitting was applied to compute rate constants expressions and these were computed as a function of the cross section. Deuterium was used instead of the hydrogen atom to investigate the effect of the mass of the target molecule and incident molecule on the cross section, reaction probability, scattering angle, and reaction rate. [ABSTRACT FROM AUTHOR]

The rate constants for the formation, destruction, and collisional excitation of SH+ are calculated from quantum mechanical approaches using two new SH+2 SH 2 + $ {\rm SH}_2^+ $ potential energy surfaces (PESs) of 4A″ and 2A″ electronic symmetry. The PESs were developed to describe all adiabatic states correlating to the SH+(3Σ−) + H(2S) channel. The formation of SH+ through the S+ + H2 reaction is endothermic by ≈9860 K, and requires at least two vibrational quanta on the H2 molecule to yield significant reactivity. Quasi-classical calculations of the total formation rate constant for H2(v = 2) are in very good agreement with the quantum results above 100 K. Further quasi-classical calculations are then performed for v = 3, 4, and 5 to cover all vibrationally excited H2 levels significantly populated in dense photodissociation regions (PDR). The new calculated formation and destruction rate constants are two to six times larger than the previous ones and have been introduced in the Meudon PDR code to simulate the physical and illuminating conditions in the Orion bar prototypical PDR. New astrochemical models based on the new molecular data produce four times larger SH+ column densities, in agreement with those inferred from recent ALMA observations of the Orion bar. [ABSTRACT FROM AUTHOR]

New adiabatic potential energy surfaces (PESs) for 2 A ′ and 2 A ″ states of SiH(X 2 Π )-He( 1 S ) complex have been calculated at the restricted coupled cluster level of theory including single, double and triple excitation [RCCSD(T)]. The RKHS method was used for the analytic fit of these PESs. The resulting PESs were employed later in the close-coupling approach for the computation of the inelastic integral cross sections which take into account the fine-structure of the SiH radical. Scattering calculations, are done on a grid of collision energies large enough to ensure converged state-to-state rate coefficients for the temperature ranging from 8 K up to 300 K. [ABSTRACT FROM AUTHOR]

The mechanism for vibrational inelastic excitation during the collision between Li2(v = 0) and Li was investigated exploiting classical trajectory simulations over a potential energy surface generated by fitting valence full configuration interaction calculations employing a large basis set. From the trajectory results, it emerges that the vibrational excitation in noncapture collisions presents uniquely a forward-scattered projectile for the highest levels of excitation (ΔE(0 → v') ≃ Ecoll). For lower v', a minor contribution presenting a backward-scattered projectile appears, which, however, has its major contribution coming from a "slingshot"-like (orbiting) mechanism exploiting the attractive features of the Li3 potential energy surface rather than a direct recoil. [ABSTRACT FROM AUTHOR]

Rotational excitation cross sections and rate coefficients for the inelastic collision of HCNO by He atom are computed at low temperature. To perform this, an interaction potential energy surface of the HCNO( X 1 Σ + )–He( 1 S ) van der Waals complex is obtained at the CCSD(T)/aug-cc-pVQZ level of theory. This potential presents a well depth of about 64.14 cm −1 below the HCNO–He dissociation limit. The cross sections are obtained in the close coupling scheme and rate coefficients inferred by averaging the cross sections over a Maxwell–Boltzmann velocity distribution. A propensity towards Δ J = 1 transitions is observed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Full quantum mechanical approach of the low-energy scattering of NO from a Cu atom on a realistic, global potential energy surface. [•] Evidence for a long lived (several hundreds of femtoseconds), transient collision complex. [•] State-of-the-art calculations using the Multi-Configurational Time-Dependent Hartree program. [•] Scattering probabilities to several channels of inelastic collisions are calculated. [•] Accuracy assessment of the calculations via investigation of microscopic reversibility. [Copyright &y& Elsevier]

Just as light scattering from an object results in diffraction patterns, the quantum mechanical nature of molecules can lead to the diffraction of matter waves during molecular collisions. This behaviour manifests itself as rapid oscillatory structures in measured differential cross-sections, and such observable features are sensitive probes of molecular interaction potentials. However, these structures have proved challenging to resolve experimentally. Here, we use a Stark decelerator to form a beam of state-selected and velocity-controlled NO radicals and measure state-to-state differential cross-sections for inelastic collisions of NO with He, Ne and Ar atoms using velocity map imaging. The monochromatic velocity distribution of the NO beam produced scattering images with unprecedented sharpness and angular resolution, thereby fully resolving quantum diffraction oscillations. We found excellent agreement with quantum close-coupling scattering calculations for these benchmark systems. [ABSTRACT FROM AUTHOR]

Recent work on collisional depolarisation in electronically excited radicals is reviewed, with a focus on the NO(A) and OH(A) radicals in collisions with rare gas atoms. The mechanism of depolarisation, and its competition with other collisional processes, is investigated using a combination of experimental and theoretical methods. The present state of the field is also put into context with other, related work in similar areas. [ABSTRACT FROM PUBLISHER]

New quantum scattering calculations for rotational deexcitation transitions of CO induced by H collisions using two CO-H potential energy surfaces (PESs) from Shepler et al. are reported. State-to-state rate coefficients are computed for temperatures ranging from 1 to 3000 K for CO(ν = 0, j) deexcitation from j = 1 to 5 to all lower j' levels, with j being the rotational quantum number. Different resonance structures in the cross sections are attributed to the differences in the anisotropy and the long-range van derWaals well depths of the two PESs. These differences affect rate coefficients at low temperatures and give an indication of the uncertainty of the results. Significant discrepancies are found between the current rate coefficients and previous results computed using earlier potentials, while the current results satisfy expected propensity rules. Astrophysical applications to modeling far infrared and submillimeter observations are briefly discussed. [ABSTRACT FROM AUTHOR]

Quantum scattering calculations on collisional rotational and vibrational energy transfer in small hydrocarbon reactive intermediates are highlighted. This review focuses on recent theoretical studies of energy transfer in methylene (CH2), in both its ground triplet3B1and low-lying singlet1A1electronic states, and in the methyl (CH3) radical. Propensities in the state-to-state cross sections are shown to depend upon the two types of anisotropies that are present in potential energy surfaces of systems involving nonlinear polyatomic molecules. Computed rate constants for rotational and vibrational relaxation are compared with available experimental data. In addition, collisional transfer between the CH2andstates is addressed. Collision-induced intersystem crossing is shown to be mediated by spectroscopically perturbed rotational levels of mixed electronic character. [ABSTRACT FROM AUTHOR]

We review recent progress in the loss or transfer of the polarisation of angular momentum in collisions of small free radicals with a thermal bath of closed-shell partners. Our primary theme is the connection between the observed behaviour and the nature of the underlying potential energy surfaces (PESs). We consider the systems NO(A2Σ+) + He and Ar; OH(A2Σ+) + He and Ar; OH(X2Π) + He, Ar and Xe; NO(X2Π) + Ar and CN(A2Π) + Ar, which vary both kinematically and in the strength of any attractive interaction. They are chosen because reliable theoretical PESs have been predicted; QS or QCT scattering calculations have been carried out; and they have been studied by recently developed experimental methods sensitive to polarisation. The efficiency of elastic depolarisation depends intimately on the competition with other, inelastic outcomes. It is generally found to be inefficient for systems dominated by impulsive forces, which promote instead changes of state. This is exacerbated by kinematic effects, in particular for the light He collision partner. Moderately attractive PESs support more efficient elastic depolarisation for low rotational levels, but this drops off rapidly with increasing rotation. Persistent elastic depolarisation across all rotational levels is a feature of deeply attractive, strongly anisotropic PESs. The 2Σ+-rare gas systems are characterised by a single controlling PES and are well described by a spin-spectator model. The 2Π-rare gas systems require two PESs, expressible as 2 A′ and 2 A′′ adiabatic surfaces or their diabatic sum and difference, V sum and V diff. Propensities rules reflecting the symmetries of these surfaces help to explain much of the detailed behaviour. [ABSTRACT FROM AUTHOR]

Rate constants for collisional loss and transfer of population and rotational angular momentum alignment have been determined for the CN(A2Π, v = 4)+Ar system. Aligned samples of CN(A2Π, v = 4, F1, j = 1.5-23.5e) were prepared by optical pumping on the A-X(4,0) band. Their evolution was observed using Doppler-resolved frequency-modulated spectroscopy in stimulated emission on the A-X(4,2) band. State-resolved total population removal rate constants, and state-to-state rotational energy transfer (RET) rate constants, are found to be in excellent agreement with previous experimental measurements and theoretical predictions for the v = 3 level. Rapid elastic depolarization of rotational alignment was observed for j = 1.5-6.5, with an average rate constant of 1.1 × 10-10 cm3 s-1. This declines with increasing j, reaching zero within experimental error for j = 23.5. The polarization transfer efficiency of the initially created alignment in state-to-state RET was also determined for the selected initial state j = 6.5, F1, e. Substantial depolarization of the alignment was observed for small Δj transitions. Alignment transfer efficiencies ranged from 0.55 ± 0.06 for Δj = -1, to 0.32 ± 0.08 for Δj = +3. These measurements are discussed with reference to recent experimental and theoretical advances on collisional depolarization of related open-shell species. We suggest that the surprisingly efficient collisional depolarization observed may be the result of the multiple potential energy surfaces involved in this system. [ABSTRACT FROM AUTHOR]

Knowledge of energy exchange rate constants in inelastic collisions is critically required for accurate characterization and simulation of several processes in gaseous environments, including planetary atmospheres, plasma, combustion, etc. Determination of these rate constants requires accurate potential energy surfaces (PESs) that describe in detail the full interaction region space and the use of collision dynamics methods capable of including the most relevant quantum effects. In this work, we produce an extensive collection of vibration-to-vibration (V–V) and vibration-to-translation/rotation (V–T/R) energy transfer rate coefficients for collisions between CO and N 2 molecules using a mixed quantum-classical method and a recently introduced (A. Lombardi, F. Pirani, M. Bartolomei, C. Coletti, and A. Laganà, Frontiers in chemistry, 7, 309 (2019)) analytical PES, critically revised to improve its performance against ab initio and experimental data of different sources. The present database gives a good agreement with available experimental values of V–V rate coefficients and covers an unprecedented number of transitions and a wide range of temperatures. Furthermore, this is the first database of V–T/R rate coefficients for the title collisions. These processes are shown to often be the most probable ones at high temperatures and/or for highly excited molecules, such conditions being relevant in the modeling of hypersonic flows, plasma, and aerospace applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high precision full-dimensional PES of H 2 CO-H 2 system was constructed in this work. • Inelastic collision energy transfer between H 2 CO and H 2 was studied using QCT method. • The histograms of energy transfer between H 2 CO and H 2 show biexponential-like decays. • Increasing collision, vibration, and rotation energy can promote the energy transfer. The inelastic collision energy transfer between H 2 CO and H 2 was investigated using QCT method based on a new accurate full-dimensional PES, which was constructed using PIP-NN method based on ∼195000 ab initio points calculated at CCSD(T)/cc-pVTZ level. The dynamic results for different collision energy, vibration and/or rotation energy of H 2 CO(H 2) show that the histograms of energy transfer obey biexponential-like decays, indicating that there exist energy transfers between H 2 CO and H 2. Moreover, the energy transfers of H 2 CO(H 2) increased with the increase of collision energy, vibration and/or rotational energy of H 2 CO(H 2). These results are beneficial to understand the intermolecular inelastic collision. [ABSTRACT FROM AUTHOR]

We report the cross sections and the transitional rates of the first 11 rotational levels of the NCO induced by collision with He at low temperatures. For this purpose, we have calculated the potential energy surface (PES), i.e transitional structure between the NCO(X1Σ) and He() by using the coupled cluster singles and doubles perturbed by triple excitations (CCSD(T)). The augmented correlation consistent polarized valence triple zeta (AVTZ) basis set to which we have associated the mid-bond functions, between the molecule and the projectile for a better description of the van der Waals interaction, was used. The PES was interpolated by the Legendre polynomials, analytically fitted, then used for the evaluation of the integral state-to-state rotational transitions cross sections in the close-coupling approach. The rate coefficients were subsequently computed for low kinetic temperature (T 150K). [ABSTRACT FROM AUTHOR]