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The absorption spectra of thin films (CsCl)1–x(CuCl)x were studied at T = 90 K in the spectral range 2–6 eV. From the analysis of the spectra, the formation of CsCu2Cl3 and Cs2CuCl3 compounds in the CsCl–CuCl system was created. The Cs2CuCl3 compound is stable only in a vacuum; in air, it apparently decomposes into CsCu2Cl3 with a disordered crystal lattice and CsCl. The exciton spectrum of both compounds is interpreted on the basis of transitions in the Cu+ ion. The one-dimensional character of excitons in CsCu2Cl3 and the two-dimensional character in Cs2CuCl3 were established. [ABSTRACT FROM AUTHOR]

We conduct polarization-dependent ultrafast spectroscopy to study the dynamics of singlet fission (SF) in tetracene single crystals. The spectrotemporal species for singlet and triplet excitons in transient absorption spectra are found to be strongly dependent on probe polarization. By carefully analyzing the polarization dependence, the signals contributed by different transitions related to singlet excitons have been disentangled, which is further applied to construct the correlation between dynamics of singlet and triplet excitons. The anisotropy of exciton dynamics provides an alternative approach to tackle the long-standing challenge in understanding the mechanism of singlet fission in organic semiconductors. [ABSTRACT FROM AUTHOR]

The geometry and infrared absorption spectrum of (RbCs)2 have been studied by full dimensional quantum dynamics simulations. For this purpose, the potential energy and dipole moment surfaces are generated by means of a cluster expansion with all two and three mode correlations, and fitted to analytical expressions with negligible deviations. Accordingly, the ground state (RbCs)2 has a diamond geometry with D2h symmetry. The infrared spectrum with frequencies up to 120 cm-1, exhibits rich details of the fundamentals, overtones, and combination bands; the highest fundamental frequency of (RbCs)2 is only 40.26 cm-1. The present study unravels important details of the interactions between the widely investigated ultracold RbCs molecules. [ABSTRACT FROM AUTHOR]

The high-frequency region was used to record the absorption spectrum of water in nanoscale pores during vacuum pumping or injection of water. The wide spectral range, which included the vibration overtones, allowed to resolve the structure of the absorption bands with variation of water concentration in the pores of SiO2. The absorption bands of water clusters in the 4570-5400 cm-1 range consist of well-resolved sub-bands with interpeak intervals of up to 580 cm-1. When the pore diameter is decreased from 11.8 to 2.6 nm, the absorption bands of clusters in this frequency range are shifted by 530 cm-1 in the direction of the water monomer which indicates an increase of hydrogen bond strength in confined water with an increase of the pore diameter. The spectrum recorded during water pumping is extremely variable in time, and the cluster dynamics in large pores (11.8 nm) differs greatly from the dynamics in small pores (2.6 nm). While all types of water clusters are removed from small pores uniformly, in the case of large pores, the water clusters relating to strong hydrogen bonds are removed from the sample at the beginning of the vacuum pumping and the loosely coupled clusters are removed later. The rate of this process is not steady and varies throughout pumping. [ABSTRACT FROM AUTHOR]

We present ultrafast transient absorption spectra of two oligofluorene derivatives in dilute solution. These spectra display a photoinduced absorption band with clear vibronic structure, which we analyze rigorously using a time-dependent formalism of absorption to extract the principal excited-state vibrational normal-mode frequencies that couple to the electronic transition, the configurational displacement of the higher-lying excited state, and the reorganization energies. We can model the excited-state absorption spectrum using two totally symmetric vibrational modes with frequencies 450 (dimer) or 400 cm-1 (trimer), and 1666 cm-1. The reorganization energy of the ground-state absorption is rather insensitive to the oligomer length at 230 meV. However, that of the excited-state absorption evolves from 58 to 166 meV between the oligofluorene dimer and trimer. Based on previous theoretical work [A. Shukla et al., Phys. Rev. B 67, 245203 (2003)], we assign the absorption spectra to a transition from the 1Bu excited state to a higher-lying mAg state, and find that the energy of the excited-state transition with respect to the ground-state transition energy is in excellent agreement with the theoretical predictions for both oligomers studied here. These results and analysis permit profound understanding of the nature of excited-state absorption in π-conjugated polymers, which are the subject of general interest as organic semiconductors in the solid state. [ABSTRACT FROM AUTHOR]

The Ã-X electronic absorption spectrum of vinoxy radical has been investigated using room temperature cavity ringdown spectroscopy. Analysis of the observed bands on the basis of computed vibrational frequencies and rotational envelopes reveals that two distinct types of features are present with comparable intensities. The first type corresponds to “normal” allowed electronic transitions to the origin and symmetric vibrations in the à state. The second type is interpreted in terms of excitations to asymmetric à state vibrations, which are only vibronically allowed by Herzberg–Teller coupling to the B state. Results of electronic structure calculations indicate that the magnitude of the Herzberg–Teller coupling is appropriate to produce vibronically induced transitions with intensities comparable to those of the normal bands. [ABSTRACT FROM AUTHOR]

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the transient species produced in gaseous reactions of CH3CO and O2; IR absorption spectra of CH3C(O)OO and α-lactone were observed. Absorption bands with origins at 1851±1, 1372±2, 1169±6, and 1102±3 cm-1 are attributed to t-CH3C(O)OO, and those at 1862±3, 1142±4, and 1078±6 cm-1 are assigned to c-CH3C(O)OO. A weak band near 1960 cm-1 is assigned to α-lactone, cyc-CH2C(==O)O, a coproduct of OH. These observed rotational contours agree satisfactorily with simulated bands based on predicted rotational parameters and dipole derivatives, and observed vibrational wavenumbers agree with harmonic vibrational wavenumbers predicted with B3LYP/aug-cc-pVDZ density-functional theory. The observed relative intensities indicate that t-CH3C(O)OO is more stable than c-CH3C(O)OO by 3±2 kJ mol-1. Based on these observations, the branching ratio for the OH+α-lactone channel of the CH3CO+O2 reaction is estimated to be 0.04±0.01 under 100 Torr of O2 at 298 K. A simple kinetic model is employed to account for the decay of CH3C(O)OO. [ABSTRACT FROM AUTHOR]

The laser-induced fluorescence spectra (both fluorescence excitation and dispersed fluorescence) of jet-cooled 1,3-benzodioxan along with its ultraviolet absorption spectra have been recorded and analyzed in order to determine the vibrational quantum levels in both the ground and S1(π,π*) electronic excited states. A detailed energy map of the vibrational levels involving the six lowest frequency vibrations was established and utilized to better understand the structural and conformational differences between the ground and excited electronic states. The energies of more than a dozen vibrational excited states involving the out-of-plane ring twisting (ν47) and the out-of-plane ring bending (ν48) modes were determined for both S0 and S1 electronic states. Ab initio and density functional theory (DFT) calculations were also carried out to complement the experimental work. The data allowed one-dimensional potential energy functions in terms of the ring-twisting coordinate to be calculated. These show the molecule to have a twisting angle of 33° and a barrier to planarity of 4300±500 cm-1 for the S0 ground state and an angle of 24° and a barrier of 1500±200 cm-1 for the S1(π,π*) excited state. [ABSTRACT FROM AUTHOR]

A general formalism for introducing nuclear quantum effects in the expression of the quantum time correlation function of an operator in a multilevel electronic system is presented in the adiabatic limit. The final formula includes the nuclear quantum time correlation functions of the operator matrix elements, of the energy gap, and their cross terms. These quantities can be inferred and evaluated from their classical analogs obtained by mixed quantum-classical molecular dynamics simulations. The formalism is applied to the absorption spectrum of a hydrated electron, expressed in terms of the time correlation function of the dipole operator in the ground electronic state. We find that both static and dynamic nuclear quantum effects distinctly influence the shape of the absorption spectrum, especially its high energy tail related to transitions to delocalized electron states. Their inclusion does improve significantly the agreement between theory and experiment for both the low and high frequency edges of the spectrum. It does not appear sufficient, however, to resolve persistent deviations in the slow Lorentzian-like decay part of the spectrum in the intermediate 2–3 eV region. [ABSTRACT FROM AUTHOR]

Pyrylium dyes having the same basic chemical structure, differing only to a specific substituent, have been used as novel materials for multiphoton three-dimensional data storage. Electronic absorption spectra, two-photon and three-photon absorption properties of this class of pyrylium dyes, have been studied theoretically and compared to experimental results. The effects of the counteranion, the surrounding solvent, and electron releasing and electron withdrawing groups in specific positions of the basic structure have been explored in detail. It is argued that on grounds of the quality of experimental spectroscopic agreement, the computed two- and three-photon data may be used in pulse propagation simulations of three-dimensional recording in optical memories. [ABSTRACT FROM AUTHOR]

Dilute-nitride GaNSb bulk materials with up to 1.4% nitrogen were grown by molecular beam epitaxy on GaSb substrates. Hall measurements indicate residual hole concentrations of nearly 1019 cm-3 at room temperature, but a decrease to below 1016 cm-3 and a hole mobility of 1300 cm2/V s at 4.5 K for a sample with 0.6% nitrogen. Photoluminescence (PL) and optical absorption measurements demonstrate a bandgap reduction by up to 300 meV with increasing nitrogen incorporation. The experimental absorption spectra are well fit by a functional dependence corresponding to direct allowed optical transitions, and the PL spectra are also consistent with that interpretation. Room temperature carrier relaxation times in the picosecond range are measured using an ultrafast PL upconversion technique. [ABSTRACT FROM AUTHOR]

The optical properties of Er3+ in polycrystalline (ceramic), and nanocrystalline forms of cubic (bixbyite) yttrium oxide are modeled based on the absorption spectra obtained between 400 and 1700 nm and the fluorescence spectra observed between 1500 and 1670 nm. Both spectra were obtained at 8 K. The observed crystal-field splitting and the measured intensities of transitions between Stark levels of the 2S+1LJ multiplet manifolds of Er3+(4f11) in both the C2 and C3i sites of Y2O3 are analyzed in terms of established models. The inversion symmetry of C3i sites limits the observed electronic transitions to magnetic dipole transitions between the 4I13/2 and 4I15/2 manifolds. There is no spectroscopic evidence for transitions involving other multiplet manifolds of Er3+ ions in C3i sites. For Er3+ ions in C2 sites, forced electric dipole transitions are allowed between the J+12 Stark levels associated with each manifold. With few exceptions, the crystal-field splitting and the intensities of the transitions between Stark levels are comparable between the nanocrystalline, polycrystalline, and the flame fusion grown crystals of cubic yttrium oxide containing trivalent erbium. [ABSTRACT FROM AUTHOR]

The diagonal linewidth in two-dimensional infrared spectra is often narrower than the distribution of transition frequencies. The width along the antidiagonal is broader than predicted by the lifetime broadening. These effects arise from time-dependent fluctuations of the transition frequencies. They can be accounted for with a semiclassical approach. For systems with many coupled vibrational modes, this approach, however, becomes computationally too demanding to be practically applicable. A time-averaging approximation was suggested for linear infrared absorption spectra. In this paper, we demonstrate that the averaging can be optimized to fit a broader scale of frequency fluctuations by using a Gaussian weight function instead of the originally proposed box function. We further generalize the time-averaging method to allow the simulation of two-dimensional infrared spectra and demonstrate the method on a simple system. The approximation delivers a large speed-up of the calculation without losing significant accuracy. [ABSTRACT FROM AUTHOR]

Two-dimensional optical spectra of J-aggregates at low temperature provide a large amount of information about the nature and dynamics of exciton states that is hidden in conventional broad band pump-probe spectra. By using numerical simulations, we study the two-dimensional absorption spectrum and find that it is dominated by a V-shaped negative peak and a blueshifted elliptic positive peak. We demonstrate a simple method to derive the energy dependence of the exciton localization size from the distance between these two features in the zero waiting time experiment. When the waiting time is turned on, the V peak is filled with an extra positive peak resulting from population relaxation. From the time evolution of this peak, energy dependent relaxation rates can be obtained. The oscillations of coherent contributions to the two-dimensional spectrum are not damped by inhomogeneous mechanisms and can be seen clearly. [ABSTRACT FROM AUTHOR]

Detailed investigation on the vibrational and electronic spectra has been carried out in order to study various properties of 2,2′-dipyridylketone molecule in its ground and excited electronic states. To get insight into the structural and symmetry features of the molecule, Raman excitation profiles of several normal modes have been analyzed. The polarized Raman spectra in different environments along with their IR counterpart have been critically surveyed and different normal modes have been assigned. The knowledge in regard to the positions of different excited electronic states has been acquired from the study of electronic absorption spectra. All the experimental observations have been substantiated and corroborated theoretically by the quantum chemical calculation. Possibility of exciton splitting of the 1La band has been explored both from theoretical and experimental points of view. [ABSTRACT FROM AUTHOR]

The absorption spectra of all-trans-β-carotene in n-hexane and carbon disulfide (CS2) solutions are measured under high pressure at ambient temperature. The common redshift and broadening in the spectra are observed. Simulation of the absorption spectra was performed by using the time-domain formula of the stochastic model. The pressure dependence of the 0-0 band wavenumber is in agreement with the Bayliss theory at pressure higher than 0.2 GPa. The deviation of the linearity at lower pressure is ascribed to the reorientation of the solvent molecules. Both the redshift and broadening are stronger in CS2 than that in n-hexane because of the more sensitive pressure dependence of dispersive interactions in CS2 solution. The effect of pressure on the transition moment is explained with the aid of a simple model involving the relative dimension, location, and orientation of the solute and solvent molecules. The implication of these results for light-harvesting functions of carotenoids in photosynthesis is also discussed. [ABSTRACT FROM AUTHOR]

Photoluminescence and absorption spectroscopy experiments are implemented on as-grown and thermally annealed GaAs1-xNx epilayers grown on GaAs(001) having a nitrogen content in the range of 0.4%–7.1%. At low temperature, photoluminescence spectra exhibit two sets of features: (i) a relatively broad peak at low energy in the vicinity of the band gap predicted by the band anticrossing model (BAC) and (ii) sharp excitonic features at higher energy (over 100 meV above the band gap for x>4%). An enhancement of the photoluminescence response of excitonic emissions and a notable intensity reduction of the deeper luminescence were systematically observed for samples subjected to high-temperature postgrowth annealing treatments. For pseudomorphically strained low nitrogen-containing epilayers (x<2%), and by taking into account the strain magnitude and the average substitutional nitrogen concentration (as extracted from x-ray analysis), excitonic energies and corresponding band gaps (as determined by absorption spectroscopy) are well described within the framework of the BAC model. The extracted binding energies of split heavy- and light-hole excitons are found to be consistent with the expected increase of electron effective masses. For thick partially relaxed epilayers (1%4%), the fundamental band gap of GaAsN is found at significantly higher energies than those predicted by the BAC model using the commonly accepted nitrogen coupling parameter CNM=2.7 eV. To account, within the BAC framework, for the apparent deceleration in the band-gap reduction rate requires the use of a smaller coupling constant (CNM=2.0 eV), which suggests a weakening of the strength of the interaction between the localized nitrogen state and the conduction band of the host matrix. This observation seems to be associated with the increasing population of N-related defects. [ABSTRACT FROM AUTHOR]

Time-dependent density-functional theory/localized density matrix method (TDDFT/LDM) was developed to calculate the excited state energy, absorption spectrum and dynamic polarizability. In the present work we generalize it to calculate the dynamic hyperpolarizabilities in both time and frequency domains. We show that in the frequency domain the 2n+1 rule can be derived readily and the dynamic hyperpolarizabilities are thus calculated efficiently. Although the time-domain TDDFT/LDM is time consuming, its implementation is straightforward because the evaluation of the derivatives of exchange-correlation potential with respect to electron density is avoided. Moreover, the time-domain method can be used to simulate higher order response which is very difficult to be calculated with the frequency-domain method. [ABSTRACT FROM AUTHOR]

Solvent effects on the two-photon absorption of a symmetrical diamino substituted distyrylbenzene chromophore have been studied using the density functional response theory in combination with the polarizable continuum model. It is shown that the dielectric medium has a rather small effect both on the bond length alternation and on the one-photon absorption spectrum, but it affects significantly the two-photon absorption cross section. It is found that both one- and two-photon absorptions are extremely sensitive to the planarity of the molecule, and the absorption intensity can be dramatically reduced by the conformation distortion. It has led to the conclusion that the experimentally observed anomalous solvent effect on the two-photon absorption of dialkylamino substituted distyrylbenzene chromophores cannot be attributed to the intrinsic properties of a single molecule and its interaction with solvents. [ABSTRACT FROM AUTHOR]

The model Hamiltonian approach of Köppel et al. [Adv. Chem. Phys. 57, 59 (1984)] is used to analyze the electronic spectroscopy of the nitrate radical (NO3). Simulations of negative ion photodetachment of NO3-, the X 2A2′←B 2E′ dispersed fluorescence spectrum of NO3, and the B 2E′←X 2A2′ absorption spectrum are all in qualitative agreement with experiment, indicating that the model Hamiltonian contains most or all of the essential physics that govern the strongly coupled X 2A2′ and B 2E′ electronic states of the radical. All 14 bands seen in the dispersed fluorescence spectrum below 2600 cm-1 are assigned based on the simulations, filling in a few gaps left by previous work, and 7 additional bands below 4000 cm-1 are tentatively assigned. The assignment is predicated on the assumption that the ν3 level of NO3 is near 1000 cm-1 rather than 1492 cm-1 as is presently believed. Support for this reassignment (which associates the 1492 cm-1 band with the ν1+ν4 level) comes from both the model Hamiltonian spectrum and a Fourier-transform infrared feature at 2585 cm-1 that is consistent with the large and positive cross anharmonicity between ν1 and ν4 needed for the alternative 1492 cm-1 assignment. An apparent systematic deficiency exists in the treatment of the model Hamiltonian for levels involving ν4. A discussion of the correlation between energy levels in the rigid D3h and C2v limits is illustrative, and provides insight into just how hard it is to treat the degenerate bending coordinate (q4) of NO3 accurately. [ABSTRACT FROM AUTHOR]

C6H5SO2 radicals were produced upon irradiation of three flowing mixtures: C6H5SO2Cl in N2, C6H5Cl and SO2 in CO2, and C6H5Br and SO2 in CO2, with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record the time-resolved infrared (IR) absorption spectra of reaction intermediates. Two transient bands with origins at 1087.7 and 1278.2 cm-1 are assigned to the SO2-symmetric and SO2-antisymmetric stretching modes, respectively, of C6H5SO2. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predict the geometry and vibrational wave numbers of C6H5SO2 and C6H5OSO. The vibrational wave numbers and IR intensities of C6H5SO2 agree satisfactorily with the observed new features. Rotational contours of IR spectra of C6H5SO2 simulated based on predicted molecular parameters agree satisfactorily with experimental results for both bands. The SO2-symmetric stretching band is dominated by a- and c-type rotational structures and the SO2-antisymmetric stretching band is dominated by a b-type rotational structure. When C6H5SO2Cl was used as a precursor of C6H5SO2, C6H5SO2Cl was slowly reproduced at the expense of C6H5SO2, indicating that the reaction Cl+C6H5SO2 takes place. When C6H5Br/SO2/CO2 was used as a precursor of C6H5SO2, features at 1186 and 1396 cm-1 ascribable to C6H5SO2Br were observed at a later period due to secondary reaction of C6H5SO2 with Br. Corresponding kinetics based on temporal profiles of observed IR absorption are discussed. [ABSTRACT FROM AUTHOR]

Using semiclassical electron-radiation-ion dynamics, the authors have examined the effect of nuclear motion, resulting from both finite temperature and the response to a radiation field, on the line broadening of the excitation profile of 2,6-pyridinedicarboxylic acid (dipicolinic acid). With nuclei fixed, there is a relatively small broadening associated with the finite time duration of an applied laser pulse. When the nuclei are allowed to move, the excitation spectrum exhibits a much larger broadening, and is also reduced in height and shifted toward lower frequencies. In both cases, the excitation is due to well-defined π to π* transitions. The further inclusion of thermal motion at room temperature broadens the linewidth considerably because of variations in the molecular geometry: Transitions that had zero or negligible transition probabilities in the ground state geometry are weakly excited at room temperature. [ABSTRACT FROM AUTHOR]

Linear and quadratic response time-dependent density functional theories have been applied to calculate the photophysical properties of donor-π-acceptor molecules which are known to have large nonlinear absorption. The linear absorption and two-photon absorption spectra predicted using hybrid functionals, including the Coulomb-attenuated model, with continuum solvation models are reported and compared to experiment and to previous theoretical predictions. While the quadratic response with these functionals overestimated the TPA cross sections relative to experiment when a Gaussian linewidth function was used, a fairly good agreement was obtained when a Lorentzian linewidth function was applied. In addition, the comparison of the TPA cross sections calculated by the sum over states with those calculated by the two-state approximation indicates the importance of the higher energy states in TPA, particularly in nondegenerate experiments. [ABSTRACT FROM AUTHOR]

Resonance Raman spectra were obtained for 2-iodothiophene in cyclohexane solution with excitation wavelengths in resonance with the A-band absorption spectrum. These resonance Raman spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion mainly along the nominal symmetric CC stretch of the thienyl ring and accompanied by a moderate amount of motion along the nominal symmetric CSC stretch, the nominal antisymmetric CSC stretch, and the nominal C-I stretch vibrational modes. A preliminary resonance Raman intensity analysis was done for the A-band resonance Raman spectra of 2-iodothiophene. These results were compared to previous results for related iodobenzene and iodoalkane molecules that also contain a C-I chromophore and the similarities and differences in the short-time photodissociation dynamics were discussed. [ABSTRACT FROM AUTHOR]

Anti-Stokes cooling has been observed in an Yb3+-doped BaY2F8 single crystal. Single crystals have been grown by the Czochralski technique. The absorption spectra and the emission properties have been measured at room temperature and at 10 K. The energy positions of the Stark sublevels of the ground and the excited state manifolds have been determined and separated from the vibronic substructure. The intrinsic decay time of the 2F5/2 level has been measured taking care of avoiding the effect of multiple reabsorption processes. The theoretical and experimental cooling efficiencies of Yb:BaY2F8 are evaluated and compared with respect to those of the most frequently investigated materials for laser cooling. A temperature drop of almost 4 K was measured by pumping the crystal with 3 W of laser radiation at ∼1025 nm in single pass configuration with a cooling efficiency of ∼3%. [ABSTRACT FROM AUTHOR]

We have investigated the ring opening of 1,3-cyclohexadiene to form 1,3,5-cis-hexatriene (Z-HT) using optical pulse shaping to enhance multiphoton excitation. A closed-loop learning algorithm was used to search for an optimal spectral phase function, with the effectiveness or fitness of each optical pulse assessed using the UV absorption spectrum. The learning algorithm was able to identify pulses that increased the formation of Z-HT by as much as a factor of 2 and to identify pulse shapes that decreased solvent fragmentation while leaving the formation of Z-HT essentially unaffected. The highest yields of Z-HT did not occur for the highest peak intensity laser pulses. Rather, negative quadratic phase was identified as an important control parameter in the formation of Z-HT. [ABSTRACT FROM AUTHOR]

The UV/visible spectra of a series of indigo derivatives have been evaluated by using ab initio methods. The combination of the Polarizable continuum model for estimating bulk solvent effects with the TD-B3LYP/6-311+G(2d,p)//B3LYP/6-311G(d,p) level of approximation, leads to an accurate description of the wavelength of maximum absorption of indigoïds compounds. Using this procedure, we have assessed the effects of both the surroundings (solvent and solid state) and the substitution pattern. For the latter, we obtained a mean absolute deviation of only 7 nm (0.02 eV) compared to experiment, for a set of 86 molecules/solvents. [ABSTRACT FROM AUTHOR]

The spectroscopic technique of threshold ion-pair production spectroscopy (TIPPS) has been applied to the triatomic molecule HCN. We have recorded the total ion-pair yield and TIPP spectra for the HCN→H++CN- process using coherent vacuum ultraviolet excitation. From the simulation of our high-resolution TIPP spectrum we have precisely measured the HCN ion-pair threshold EIP0 to be 122 244±4 cm-1. This value could be used to determine the bond dissociation energy D0(H-CN) to unprecedented accuracy. Our fitting result also showed that rotationally excited instead of cold CN- fragment is favored as the ion-pair dissociation product in the threshold region. [ABSTRACT FROM AUTHOR]

We have investigated theoretically the interband excitonic absorption spectra and the coupling behaviors of coupled symmetric triple Zn1-xCdxSe/ZnSe quantum wells with diluted Mn doping in the central well under external magnetic field. The results show that the magnetic field can effectively adjust the energy levels and the optical properties of the coupled multiple quantum wells (CMQWs). The coupling behaviors of the CMQWs are very sensitive to the central well depth. The effect of the magnetic-field-introduced parabolic-confined potential on the main features of the absorption spectra can be neglected at moderate magnetic-field densities. [ABSTRACT FROM AUTHOR]

Irradiation of a Ne matrix sample containing NO and CO near 4 K with an ArF excimer laser at 193 nm yielded new lines at 2045.1 and 968.0 cm-1 that were depleted upon secondary photolysis at 308 nm. These lines are assigned to C==O stretching and mixed stretching modes of ONCO, based on results of 15N-, 13C-, and 18O-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP and PW91PW91/aug-cc-pVTZ) predict five stable isomers of NCO2: ONCO, NCOO, N-cyc-CO2, CNOO, and cyc-CNOO, listed in order of increasing energy. According to B3LYP calculations, ONCO has a trans configuration, with bond angles of ∠ONC≅136.3° and ∠NOC≅160.7°. Calculated vibrational wave numbers, IR intensities, 15N-, 13C-, and 18O-isotopic shifts for ONCO agree satisfactorily with experimental results. ONCO was formed from reaction of CO with NO in its excited state. [ABSTRACT FROM AUTHOR]

We theoretically study the temperature dependence of the J-band width in disordered linear molecular aggregates, caused by dephasing of the exciton states due to scattering on vibrations of the host matrix. In particular, we consider inelastic one- and two-phonon scatterings between different exciton states (energy-relaxation-induced dephasing), as well as the elastic two-phonon scattering of the excitons (pure dephasing). The exciton states follow from numerical diagonalization of a Frenkel exciton Hamiltonian with diagonal disorder; the scattering rates between them are obtained using the Fermi golden rule. A Debye-type model for the one- and two-phonon spectral densities is used in the calculations. We find that, owing to the disorder, the dephasing rates of the individual exciton states are distributed over a wide range of values. We also demonstrate that the dominant channel of two-phonon scattering is not the elastic one, as is often tacitly assumed, but rather comes from a similar two-phonon inelastic scattering process. In order to study the temperature dependence of the J-band width, we simulate the absorption spectrum, accounting for the dephasing-induced broadening of the exciton states. We find a power-law (Tp) temperature scaling of the effective homogeneous width, with an exponent p that depends on the shape of the spectral density of the host vibrations. In particular, for a Debye model of vibrations, we find p≈4, which is in good agreement with the experimental data on J aggregates of pseudoisocyanine [I. Renge and U. P. Wild, J. Phys. Chem. A, 101, 7977 (1997)]. [ABSTRACT FROM AUTHOR]

The intermolecular arrangement in the solid state and the consequences on the optical and photophysical properties are studied on different derivatives of oligophenylenevinylenes by UV/VIS absorption and angular-resolved polarized fluorescence spectroscopy. Unsubstituted distyrylbenzene (DSB) organizes in a herringbone manner, with the long axes of the molecules oriented in parallel, but the short axes almost perpendicular to each other. Fluorinated distyrylbenzene (F12DSB) as well as the DSB:F12DSB cocrystals prefer cofacial π-stacking in the solid state. For all structures, the consequence of the parallel alignment of the transition moments is a strongly blueshifted H-type absorption spectrum and a low radiative rate constant kF. Significant differences are observed for the emission spectra: the perpendicular arrangement of the short axes in DSB crystals leads to only very weak intermolecular vibronic coupling. Hence the emission spectrum is well structured, very similar to the one in solution. For F12DSB and DSB:F12DSB, the cofacial arrangement of the adjacent molecules enables strong intermolecular vibronic coupling of adjacent molecules. Thus, an unstructured and strongly redshifted excimerlike emission spectrum is observed. The differences in the electronic nature of the excited states are highlighted by quantum-chemical calculations, revealing the contribution of interchain excitations to the electronic transitions. [ABSTRACT FROM AUTHOR]

Far-infrared-absorption spectroscopy is used to investigate the low-frequency (<=100 cm-1) intermolecular interactions in liquid methanol. Using an intense source of far-infrared radiation, modes are elucidated at approximately 30 and 70 cm-1 in the absorption spectrum. These modes are believed to arise from intermolecular bending and librational motions, respectively, and are successfully reproduced in an ab initio molecular-dynamics simulation of methanol. [ABSTRACT FROM AUTHOR]

We use a multilevel path integral Monte-Carlo (PIMC) method to simulate the arrangement of He atoms around a single Al atom doped in a He cluster. High-level ab initio Al-He pair potentials and a Balling and Wright pairwise Hamiltonian model are used to describe the full potential and the electronic asymmetry arising from the open-shell character of the Al atom in its ground and excited electronic states. Our calculations show that the doping of the Al 3p electron strongly influences the He packing. The results of the PIMC simulation are used to predict the electronic excitation spectrum of an Al atom embedded in He clusters. With inclusion of tail corrections for the ground and excited states potentials, the calculated 3d←3p spectrum agrees reasonably well with the experimental spectrum. The blueshift of the calculated spectrum associated with the 4s←3p transition of solvated Al is about 25 nm (2000 cm-1) larger than seen in experiments on Al embedded in bulk liquid He. We predict that the spectrum associated with the 4p←3p transition will be blueshifted by ∼7000 cm-1 (nearly 1 eV). [ABSTRACT FROM AUTHOR]

Transparent copper nanorod/nanowire arrays and anodic alumina oxide composite films have been prepared by alternating current electrodeposition, and their linear optical properties have been systematically characterized by absorption spectra. In the experimental spectra, there exist transverse and longitudinal resonance peaks, which are caused by the surface-plasmon resonance along the diameter and the length of the copper nanorods, respectively. The transverse resonance peak is affected by the diameter and aspect ratio of the nanorod. The longitudinal resonance peak appears at longer wavelength when a polarized light illuminates the film with an angle of incidence of about 70°, where the angle is defined with respect to the surface normal. Moreover, the longitudinal resonance mode is sensitive to the polarization direction when compared with the transverse resonance mode. [ABSTRACT FROM AUTHOR]

In this work we present an all-Cartesian reaction surface approach, where the large amplitude coordinates span the so-called reaction plane, that is, the unique plane defined by the two minima and the saddle-point structure of an isomerization reaction. Orthogonal modes are treated within harmonic approximation which gives the total Hamiltonian an almost separable form that is suitable for multidimensional quantum dynamics calculations. The reaction plane Hamiltonian is constructed for the H-atom transfer in tropolone as an example for a system with an intramolecular O...H–O hydrogen bond. We find ground-state tunneling splittings of 3.5 and 0.16 cm-1 for the normal and deuterated species, respectively. We calculated infrared-absorption spectra for a four-dimensional model focusing on the low-frequency region. Here, we identify a reaction mode which is closely connected to the tautomerization that is reflected in the increase of tunneling splitting to 18 cm-1 upon excitation. [ABSTRACT FROM AUTHOR]

The Cn+ n=7–9 cations were produced by electron-impact ionization of perchloronaphthalene, mass selected, and their electronic absorption spectra in 6 K neon matrices recorded. The linear and cyclic isomers of C7+ and C8+ are detected. Three systems of linear C7+ are observed with origin bands near 770, 332, and 309 nm. The cyclic C7+ shows two transitions near 676 and 448 nm. One system of linear C9+ is observed commencing at 371 nm. Linear C8+ shows five dipole-allowed electronic transitions from the X 2Πg ground state, and the strongest ones have the origin bands at 890.8 and 308.1 nm. Five electronic transitions of cyclic C8+ are also discernible. [ABSTRACT FROM AUTHOR]

The three lowest (12A′, 22A′, and 12A″) potential-energy surfaces of the C2Cl radical, correlating at linear geometries with 2Σ+ and 2Π states, have been studied ab initio using a large basis set and multireference configuration-interaction techniques. The electronic ground state is confirmed to be bent with a very low barrier to linearity, due to the strong nonadiabatic electronic interactions taking place in this system. The rovibronic energy levels of the 12C12C35Cl isotopomer and the absolute absorption intensities at a temperature of 5 K have been calculated, to an upper limit of 2000 cm-1, using diabatic potential-energy and dipole moment surfaces and a recently developed variational method. The resulting vibronic states arise from a strong mixture of all the three electronic components and their assignments are intrinsically ambiguous. [ABSTRACT FROM AUTHOR]

Resonance Raman and resonance hyper-Raman spectra of the “push-pull” conjugated molecule 1-(4′-dihexylaminostyryl)-4-(4″-nitrostyryl)benzene in acetone have been measured at excitation wavelengths from 485 to 356 nm (two-photon wavelengths for the nonlinear spectra), resonant with the first two bands in the linear absorption spectrum. The theory of resonance hyper-Raman scattering intensities is developed and simplified using assumptions appropriate for intramolecular charge-transfer transitions of large molecules in solution. The absorption spectrum and the Raman, hyper-Rayleigh, and hyper-Raman excitation profiles, all in absolute intensity units, are quantitatively simulated to probe the structures and the one- and two-photon transition strengths of the two lowest-energy allowed electronic transitions. All four spectroscopic observables are reasonably well reproduced with a single set of excited-state parameters. The two lowest-energy, one-photon allowed electronic transitions have fairly comparable one-photon and two-photon transition strengths, but the higher-energy transition is largely localized on the nitrophenyl group while the lower-energy transition is more delocalized. [ABSTRACT FROM AUTHOR]

The absorption spectrum of N2, just above the first ionization limit, in the region between 125 750 and 126 600 cm-1, is dominated by two broad features which have the appearance of the towers of a “cathedral.” Recently, this energy region has been measured by Sommavilla et al. [J. Phys. B 35, 3901 (2002)] with a resolution of 0.04 cm-1 and an assignment for one of these two bands has been suggested. In order to discuss this assignment, we have solved the coupled-channel Schrödinger equation with the parameters of Spelsberg and Meyer above the v=28 level of the b′ 1∑u+ state for determining the high levels of b′. Furthermore, we evaluate the autoionization widths and the rotational structure of the different possible assignments. Finally, we propose as assignment for the second tower of the cathedral the Rydberg state (A 2Πuv+=1)3′d′σg1Πu. [ABSTRACT FROM AUTHOR]

We investigate the usefulness of a frozen-density embedding scheme within density-functional theory [J. Phys. Chem. 97, 8050 (1993)] for the calculation of solvatochromic shifts. The frozen-density calculations, particularly of excitation energies have two clear advantages over the standard supermolecule calculations: (i) calculations for much larger systems are feasible, since the time-consuming time-dependent density functional theory (TDDFT) part is carried out in a limited molecular orbital space, while the effect of the surroundings is still included at a quantum mechanical level. This allows a large number of solvent molecules to be included and thus affords both specific and nonspecific solvent effects to be modeled. (ii) Only excitations of the system of interest, i.e., the selected embedded system, are calculated. This allows an easy analysis and interpretation of the results. In TDDFT calculations, it avoids unphysical results introduced by spurious mixings with the artificially too low charge-transfer excitations which are an artifact of the adiabatic local-density approximation or generalized gradient approximation exchange-correlation kernels currently used. The performance of the frozen-density embedding method is tested for the well-studied solvatochromic properties of the n→π* excitation of acetone. Further enhancement of the efficiency is studied by constructing approximate solvent densities, e.g., from a superposition of densities of individual solvent molecules. This is demonstrated for systems with up to 802 atoms. To obtain a realistic modeling of the absorption spectra of solvated molecules, including the effect of the solvent motions, we combine the embedding scheme with classical molecular dynamics (MD) and Car-Parrinello MD simulations to obtain snapshots of the solute and its solvent environment, for which then excitation energies are calculated. The frozen-density embedding yields estimated solvent shifts in the range of 0.20–0.26 eV, in good agreement with experimental values of between 0.19 and 0.21 eV. [ABSTRACT FROM AUTHOR]

Optical-absorption and photoluminescence (PL) spectra have been measured on the defect-chalcopyrite-type semiconductor CdGa2Te4 in the 0.9–1.5-eV photon-energy range at temperatures between 11 and 300 K. The temperature dependence of the direct-gap energy of CdGa2Te4 has been determined from the optical-absorption spectra and fit using the Varshni equation and an analytical four-parameter expression developed for the explanation of the band-gap shrinkage effect in semiconductors. The PL spectra show an asymmetric emission band peaking at ∼1.326 eV and a symmetric emission band at ∼1.175 eV at T=11 K, which are attributed to donor-acceptor-pair recombination between exponentially tailed or Gaussian-like donor states and acceptor levels, respectively. A multiple-exponential fit analysis of the PL emission suggests acceptor levels of 50 and 86 meV and a deep donor level of 190 meV, together with an unidentified shallow level of 9 meV. An energy-band scheme has been proposed for the explanation of PL emission observed in CdGa2Te4. [ABSTRACT FROM AUTHOR]

An emission spectrum of hot water with a temperature of about 3000 K is obtained using an oxy-acetylene torch. This spectrum contains a very large number of transitions. The spectrum, along with previous cooler laboratory emission spectra and an absorption spectrum recorded from a sunspot, is analyzed in the 500–2000 cm-1 region. Use of a calculated variational linelist for water allows significant progress to be made on assigning transitions involving highly excited vibrational and rotational states. In particular emission from rotationally excited states up to J=42 and vibrational levels with up to eight quanta of bending motion are assigned. [ABSTRACT FROM AUTHOR]

The temporal behavior of optical response functions (ORFs) reflects the quantum dynamics of an electronic superposition state, and as such lacks a well-defined classical limit. In this paper, we consider the importance of accounting for the quantum nature of the dynamics when calculating ORFs of different types. To this end, we calculated the ORFs associated with the linear absorption spectrum and the nonlinear two-pulse photon-echo experiment, via the following approaches: (1) the semiclassical forward-backward approach; (2) an approach based on linearizing the path-integral forward-backward action in terms of the difference between the forward and backward paths; (3) an approach based on ground state nuclear dynamics. The calculations were performed on a model that consists of a two-state chromophore solvated in a nonpolar liquid. The different methods were found to yield very similar results for the absorption spectrum and “diagonal” two-pulse photon echo (i.e., the homodyne-detected signal at time t=t0 after the second pulse, where t0 is the time interval between the two pulses). The different approximations yielded somewhat different results in the case of the time-integrated photon-echo signal. The reasons for the similarity between the predictions of different approximations are also discussed [ABSTRACT FROM AUTHOR]

The structures and energetics of Li6+, Li6- and three isomers of Li6 are investigated using the coupled-cluster singles, doubles and perturbative triples [CCSD(T)] method with valence and core-valence correlation consistent basis sets of double- to quadruple-ζ quality (cc-pVXZ and cc-pCVXZ, where X=D-Q). These results are compared with qualitatively different predictions by less reliable methods. Our results conclusively show that the D4h isomer is the global minimum structure for Li6. It is energetically favored over the C5v and D3h structures by about 5.1 and 7.1 kcal mol-1, respectively, after the inclusion of the zero-point vibrational energy (ZPVE) correction. Our most accurate total atomization energies are 123.2, 117.6, and 115.7 kcal mol-1 for the D4h, C5v, and D3h isomers, respectively. Comparison of experimental optical absorption spectra with our computed electronic spectra also indicate that the D4h isomer is indeed the most stable structure. The cation, anion, and some higher spin states are investigated using the less expensive cc-pCVDZ basis set. Adiabatic ionization energies and electron affinities are reported and compared with experimental values. Predictions of molecular properties are found to be sensitive to the basis set used and to the treatment of electron correlation. [ABSTRACT FROM AUTHOR]

We study the relationship between the optical gap and the optical-absorption tail breadth for the case of amorphous gallium arsenide (a-GaAs). In particular, we analyze the optical-absorption spectra corresponding to some recently prepared a-GaAs samples. The optical gap and the optical-absorption tail breadth corresponding to each sample is determined. Plotting the optical gap as a function of the corresponding optical-absorption tail breadth, we note that a trend, similar to that found for the cases of the hydrogenated amorphous silicon and hydrogenated amorphous germanium, is also found for the case of a-GaAs. The impact of alloying on the optical-absorption spectrum associated with a-GaAs is also briefly examined. [ABSTRACT FROM AUTHOR]

Infrared absorption spectroscopy of few hundred H3+ ions trapped in a 22-pole ion trap is presented using chemical probing as a sensitive detection technique down to the single ion level. By exciting selected overtone transitions of the (v1=0,v2l=31)←(0,00) vibrational band using an external cavity diode laser an accurate diagnostics measurement of the effective translational and rotational temperatures of the trapped ions was performed. The absolute accuracy of the measured transition frequencies was improved by a factor of four compared to previous plasma spectroscopy measurements using velocity modulation [Ventrudo et al., J. Chem. Phys. 100, 6263 (1994)]. The observed buffer gas cooling conditions in the ion trap indicate how to cool trapped H3+ ions into the lowest ortho and para rotational states. Future experiments will utilize such an internally cold ion ensemble for state-selected dissociative recombination experiments at the heavy ion storage ring Test Storage Ring (TSR). © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Resonance Raman profiles for 14 vibrational modes of betaine-30 in ethanol at room temperature were measured at wavelengths within the first charge-transfer absorption band. The absorption spectrum and resonance Raman profiles were analyzed using time-dependent theory and a Brownian oscillator model modified to account for nonlinear solvent response; i.e., dependence of the solvent reorganization energy on the electronic state of the solute. As in our previous study of betaine-30 in acetonitrile, the solvent reorganization energy for the excited electronic state, determined from resonance Raman spectroscopy, was found to be smaller than that for the ground electronic state, determined from the absorption spectrum. The mode-dependent internal reorganization energies of betaine-30 in ethanol were found to be slightly larger than those of betaine-30 in acetonitrile. Temperature-dependent solvent reorganization energies for the ground electronic state were determined from analysis of the absorption line shape from 279 to 332 K and were found to decrease with increasing temperature. The influence of hydrogen bonding on the solvent and internal reorganization energy of betaine-30 is considered, and the physical basis for nonlinear solvent response is discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A general formulation of nonperturbative quantum dynamics of solutes in a condensed phase is proposed to calculate linear and nonlinear vibrational line shapes. In the weak solute-solvent interaction limit, the temporal absorption profile can be approximately factorized into the population relaxation profile from the off-diagonal coupling and the pure-dephasing profile from the diagonal coupling. The strength of dissipation and the anharmonicity-induced dephasing rate are derived in Appendix A. The vibrational energy relaxation (VER) rate is negligible for slow solvent fluctuations, yet it does not justify the Markovian treatment of off-diagonal contributions to vibrational line shapes. Non-Markovian VER effects are manifested as asymmetric envelops in the temporal absorption profile, or equivalently as side bands in the frequency domain absorption spectrum. The side bands are solvent-induced multiple-photon effects which are absent in the Markovian VER treatment. Exact path integral calculations yield non-Lorentzian central peaks in absorption spectrum resulting from couplings between population relaxations of different vibrational states. These predictions cannot be reproduced by the perturbative or the Markovian approximations. For anharmonic potentials, the absorption spectrum shows asymmetric central peaks and the asymmetry increases with anharmonicity. At large anharmonicities, all the approximation schemes break down and a full nonperturbative path integral calculation that explicitly accounts for the exact VER effects is needed. A numerical analysis of the O–H stretch of HOD in D2O solvent reveals that the non-Markovian VER effects generate a small recurrence of the echo peak shift around 200 fs, which cannot be reproduced with a Markovian VER rate. In general, the nonperturbative and non-Markovian VER contributions have a stronger effect on nonlinear vibrational line shapes than on linear absorption.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We describe the implementation of a simple technique to simulate core-level spectra within the Car-Parrinello plane-waves molecular dynamics framework. The x-ray absorption (XA) spectra are generated using the transition potential technique with the effect of the core hole included through a specifically developed pseudopotential for the core-excited atom. Despite the lack of 1s core orbitals in the pseudopotential treatment, the required transition moments are accurately calculated without reconstruction of the all-electron orbitals. The method is applied to the oxygen XA spectra of water in its various aggregation states, but it is transferable to any first-row element. The computed spectra are compared favorably with the results from all-electron cluster calculations, as well as with experimental data. The periodicity of the plane-wave technique improves the description of condensed phases. The molecular dynamics simulation enables in principle a proper treatment of thermal effects and dynamical averaging in complex systems. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]