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The low resolution vapour phase infrared spectrum of acetamide has been recorded over the range 1800–1200 cm −1 . The spectrum is complicated due to the presence of two internal rotors CH 3 and NH 2 . In the present work, few clear band contours have been identified. The structural parameters, vibrational wavenumbers, rotational constants and the transition dipole moment vectors of the vibrational modes have been estimated from the density functional theory calculations. The PR separations have been measured and compared with the quasi-rigid model of band envelopes. The optimized molecular geometry, vibrational frequencies, rotational constants, dipole moment of acetamide have been investigated using density functional theory (DFT) at the B3LYP level with basis set 6-311 ++ G(d,p). The results of the DFT calculations were used (i) to analyze the experimental PQR structures in the A, B, C and A/B type band envelopes for six vibrational modes in different regions, (ii) to estimate the barrier to internal rotation of internal rotors CH 3 and (iii) to calculate tilt angle of the CH 3 rotor’s axis. The results are in good agreement with the experimental values.

Femtosecond pump-degenerate four-wave mixing (DFWM) spectroscopy was used to investigate the dynamics in the excited B state of bromine via transitions to ion-pair states. By varying the DFWM wavelength different vibrational energy spacings of the excited B state can be observed. This arises from a substantial contribution of a hot vibrational state of the electronic ground state. Specific Franck–Condon overlaps between the B and an ion-pair state can be used to probe different parts of the excited state dynamics individually and therefore indirectly the contributions from different vibrational states in the electronic ground state. To understand the details of this complex scenario, quantum dynamical calculations were performed.

We report the CO 2 -induced broadening coefficients and line strength parameters of water vapor rovibrational transitions belonging to the (2 ν 1 + ν 2 + ν 3 ) overtone band measured by using an NIR diode laser spectrometer. Rotational quantum number dependence of the broadening coefficients is also shown. Use of balanced photodetector and wavelength modulation spectroscopy with small current modulation amplitude helped to obtain improved S / N ratio of the spectra. The recorded line shapes are fitted with standard Voigt profile by using a non-linear least squares fitting program to extract the line shape parameters.

We present Spitzer spectra of S stars, which are cool evolved stars with a C/O ratio near unity, some of which have enhanced s-process abundances. We present the detection of a strong and unusual band in themid- infrared, at 13 mu m, within the N-band window. Using quantum-chemically calculated line lists, and model spectra, we identify this band as the fundamental rovibrational band of SiS. Detection of the overtone band at 6.7 mu m confirms the identification. Fitting the line profile shows that the molecule is located in relatively cool layers, at T similar to 1500 K. We discuss these results in the context of chemical equilibrium models. The observed strength of these bands in the cool S stars makes them a promising observational diagnostic tool for studying the atmospheres of brown dwarfs and exoplanets.

The relation between the non-adiabatic vibrational correction to the reduced mass, i.e. the vibrational g-factor, and the electric dipole moment gradient of a diatomic molecule is investigated. An explicit expression for the “irreducible” non-adiabatic contribution in terms of excited electronic states is derived. The importance of this expression for the analysis of vibration-rotational spectra of diatomic molecules is discussed and explicit expressions are presented for the first two fitting parameters in an expansion of the non-adiabatic vibrational term in an effective vibration-rotational Hamiltonian. Results of ab initio multiconfigurational self consistent field calculations of the non-adiabatic contribution to vibrational g-factor of hydrides and fluorides of Li, B, Al, Ga and monoxides of C, Si and Ge are presented and compared with the corresponding non-adiabatic contributions to the rotational g-factor.

An efficient method is presented to calculate the intra-molecular potential energies and electrical dipole moments of CO2 molecules at the electronic ground state by solving the Kohn–Sham (KS) equation for a total of 101 992 nuclear configurations. The projector-augmented wave (PAW) exchange-correlation potential functionals and plane wave (PW) basis functions were used in solving the KS equation. The calculated intra-molecular potential function was then included in the pure vibrational Schrodinger equation to determine the vibrational energy eigen values and eigen functions. The vibrational wave functions combined with the calculated dipole moment function were used to determine the transition dipole moments. The calculated results were compared with the experimental data.

The three-dimensional vibrational problem for the isolated van der Waals complex formed by the Li+ cation with the N2 molecule is solved by the variational method. The potential energy and dipole moment surfaces are calculated using different basis sets of atomic functions and different approaches for taking electron correlation into account. The anharmonic effects caused by the interaction of vibrational degrees of freedom of the complex are consistently considered for the first time. The energy levels of three-dimensional vibrational states are determined. The frequency shift of the N2 molecule vibration upon complexation and the fundamental transition intensity for this vibration in the complex are calculated. The frequencies and intensities for a number of spectral transitions between the states associated with excitation of low-frequency modes are determined. The average values of geometrical parameters and their variances are calculated for the ground state and excited vibrational states of the complex.

High-resolution (ca. 0.0025 cm−1) Fourier transform infrared spectra of AsH2D were recorded in the regions of the As–H and As–D stretching fundamental bands ν1/ν5 and ν2, respectively, and analyzed. Strong resonance interactions between the bands ν1 and ν5, and also between the band ν2 and the bending overtone band 2ν4 were established. From transitions observed in the ν1 and ν5 bands ground state rotational energies for larger values of rotational quantum numbers than previously available could be determined. Thereof improved ground state rotational parameters were derived. More than 3200 assigned transitions corresponding to 1059 upper state energy levels which were almost equally distributed over the three stretching states were fitted with an rms-deviation of 0.00031 cm−1, which corresponds to experimental precision.

The Fourier transform gas-phase infrared spectrum of pyrrole, C4H5N, has been recorded with a resolution of ca. 0.003 cm−1 in the 900–1500 cm−1 spectral region. Four fundamental bands, ν8(A1; 1016.9 cm−1), ν23(B2; 1049.1 cm−1), ν7(A1; 1074.6 cm−1), ν20(B2; 1424.4 cm−1) and the overtone band 2ν16(A1; 962.7 cm−1) have been analysed using the Watson model. The ν8 and 2ν16 bands are unperturbed; the ν7 and ν23 bands are locally perturbed, while the ν20 band is globally perturbed by weak c-Coriolis resonance. Upper state vibrational term values, and rotational and centrifugal distortion constants, have been obtained from fits using S-reduction and Ir-representation as well as A-reduction and IIIr-representation. A set of ground state rotational and centrifugal distortion constants using A-reduction was obtained from a simultaneous fit of ground state combination differences from all five bands and previous microwave and millimetre-wave data.

Using a high-resolution tunable diode laser photoacoustic spectrometer, self-, N 2 and O 2 pressure broadening coefficients for the first 11 transitions of 12 C 16 O 2 in the R branch of the (30012) ← (00001) overtone band at the 6348 cm −1 have been revisited at room temperature (∼298 K). Air-broadening parameters have also been calculated from the N 2 and O 2 measurements. The dependence of the broadening on rotational quantum number m is discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficients of carbon dioxide transitions. The results are compared to our previous measurements and to the values reported in the HITRAN04 database and by other research group with a different spectroscopic technique.

The absorption spectra of acetylene molecules was measured under jet-cooled conditions in the wavelength range of 142.8152.3 nm, with a tunable and highly resolved vacuum ultraviolet (VUV) laser generated by two-photon resonant four wave difference frequency mixing processes. Due to the sufficient vibrational and rotational cooling effect of the molecular beam and the higher resolution VUV laser, the observed absorption spectra exhibit more distinct spectral features than the previous works measured at room temperature. The major three vibrational bands are assigned as a C-C symmetry stretching vibrational progress (u2 = 02) of the C1 IIu state of acetylene. The observed shoulder peak at 148.2 nm is assigned to the first overtone band of the trans-bending mode u4 of the C1 IIustate of acetylene. Additionally, the two components, 4o2(1IIu) and 4o2(1 IIuare suggested to exhibit in the present absorption spectra, due to their RennerTeller effect and transition selection rule. All band origins and bandwidths ...

Bonding, vibrational and magnetic properties of the cage-like molecule C24O12 are studied by DFT calculations. Infrared- and Raman-active vibrational frequencies of the cage-like molecule C24O12 are assigned. Two 13C and one 17O nuclear magnetic resonance (NMR) spectral signals of the cage-like molecule C24O12 are characterized. Heat of formation of the cage-like molecule C24O12 is estimated. Compared to C60 and the cage-like molecule C24O12, only from the thermodynamic points of view, C24O12 is more stable than C60. Thus we believe that the cage-like molecule C24O12 has sufficient stability to allow its experimental preparation. We proposed that it could be synthesized by using the condensation of molecules C6(OH)6 and C12Cl12. Since the symmetry of C24O12 is D6, it is a chiral molecule.

The stretching and bending vibrational energies of SnBr4 and CCl4 are calculated in the one-dimensional framework. The dynamical symmetry group of tetrahedral molecule was taken into consideration to construct the model Hamiltonian in this framework. Casimir and Majorana invariant operators were also determined accordingly. Using the model Hamiltonian so constructed, we reported the vibrational energy levels of SnBr4 and CCl4 molecules accurately.

A recent investigation and assignment of the IR spectrum of liquid toluene between 400 and 4000 cm −1 by Keefe and coworkers [J.E. Bertie, Y. Apelblat, C.D. Keefe, J. Mol. Struct. 750 (2005) 78] has been reexamined theoretically using the scaled quantum mechanical (SQM) force field method. It is proposed that three bands – a weak, broad shoulder at 947 cm −1 assigned as a combination band, an unassigned feature at 1467 cm −1 and a medium broad band at 2979 cm −1 , also assigned as a combination band – are all in fact fundamentals. Agreement with the remaining assignments is excellent, with an average deviation between the observed and theoretically predicted vibrational fundamentals of just 5.28 cm −1 . The overall intensity pattern of the experimental spectrum is also well reproduced. Analysis involving free rotation of the methyl group and interpretation of the vibrational spectrum in terms of C 2v symmetry for the phenyl ring and C 3v for the methyl group very likely contributed to the experimental misassignments.

The dynamics of overtone-excited pyruvic acid (PA) is studied using a combination of experimental and theoretical methods. It is experimentally observed that high overtone excitation of the OH-stretching mode of PA in the gas phase leads to a unimolecular decarboxylation reaction. An RRKM analysis of the rate is consistent with previous experiments for the thermal reaction but is inconsistent with the present overtone chemistry; from this it is concluded that the overtone-induced reaction is likely to be a direct reaction. Using a Fourier transform infrared spectrometer and a cavity ring-down spectrometer, the spectrum for the OH-stretch fundamental and overtone transitions is measured. We assign two conformers of PA in the spectrum, the Tc and Tt, corresponding to distinct orientations of the OH-group. The spectral peaks for the Tc-conformer broaden dramatically at the third and fourth overtones while those of the Tt-conformer remain relatively narrow. Using a three-mode quantum mechanical model for the vibrational states, the line positions and intensities are well reproduced by theory. The line widths, and the associated dynamical interpretation, are provided by a direct dynamics calculation, where the potential is computed "on-the-fly" and all degrees of freedom are included. It is found that the line broadening is due to the onset of H-atom chattering between the two O-atoms, an effect that occurs for the Tc-conformer but not the Tt-conformer. This H-atom-transfer process is the first step of the decarboxylation reaction mechanism, which subsequently involves breaking the C-C bond. The theoretical and experimental line widths agree but do not correspond to the full reaction time which is much longer than the initial chattering step.

The O-H stretching vibrational overtone spectrum of the water dimer has been calculated with the dimer modeled as two individually vibrating monomer units. Vibrational term values and absorption intensities have been obtained variationally with a computed dipole moment surface and an internal coordinate Hamiltonian, which consists of exact kinetic energy operators within the Born-Oppenheimer approximation of the monomer units. Three-dimensional ab initio potential energy and dipole moment surfaces have been calculated using the internal coordinates of the monomer units using the coupled cluster method including single, double, and perturbative triple excitations [CCSD(T)] with the augmented correlation consistent valence triple zeta basis set (aug-cc-pVTZ). The augmented correlation consistent valence quadruple zeta basis set (aug-cc-pVQZ), counterpoise correction, basis set extrapolation to the complete basis set limit, relativistic corrections, and core and valence electron correlations effects have been included in one-dimensional potential energy surface cuts. The aim is both to investigate the level of ab initio and vibrational calculations necessary to produce accurate results when compared with experiment and to aid the detection of the water dimer under atmospheric conditions.

Optical–optical double resonance spectroscopy is used to obtain total rate constants, electronic branching ratios, and vibrational product state distributions for non-adiabatic transitions among the first-tier ion-pair states of the I 2 molecule excited to the E 0 g + , v E = 8 , 13 , 19 ; J E ≈ 55 rovibronic levels in collisions with M = CD 3 I and CH 3 COCH 3 . It is shown that I 2 ( E → M D ) near-resonant transitions are caused by the interaction between the transition dipole moment of I 2 (E–D) and the permanent electric dipole moment of M . The I 2 (D) state vibrational levels populated due to polarization interaction accompanied by quasi-resonance excitation of the collision partner are also observed.

Pressure-induced foreign-broadening lineshape parameters of the carbon dioxide rovibrational transitions belonging to the (30012)←(00001) overtone band near the 1.573 μm wavelength region are measured by using a tunable diode laser photoacoustic spectrometer. The spectroscopic analysis has concerned the first 11 lines of the R branch. For these lines, the air- and Ar-broadening coefficients are measured at room temperature (∼298 K). The measured broadening coefficients of all the transitions of 12 C 16 O 2 are compared with those given in the HITRAN04 database and former measurements with a different spectroscopic method. Agreements and discrepancies are underlined and briefly discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficient of carbon dioxide transitions.

The vibronic structure of p -fluoroanisole in the first excited state (S 1 ) has been investigated with mass selected resonance-enhanced two photon ionization spectroscopy. The band origin of S 1 ← S 0 transition of p -fluoroanisole is measured to be 35149 cm −1 , which is red-shifted by 1234 cm −1 with respect to that of anisole. Combining with the ab initio calculations, the measured frequencies 397, 487, 559, 840 and 1150 cm −1 in the S 1 state are assigned as the in-plane ring vibrational mode 9 b , 6 a , 6 b , 1 and 9 a , respectively. The optimized molecular geometries and vibrational frequencies of p -fluoroanisole in the ground state (S 0 ) and cation ground state (D 0 ) are also achieved from DFT calculations.

Quantum control spectroscopy (QCS) is used as a tool to study, address selectively and enhance vibrational wavepacket motion in large solvated molecules. By contrasting the application of Fourier-limited and phase-modulated excitation on different electronic states, the interplay between the controllability of vibrational coherence and electronic resonance is revealed. We contrast control on electronic ground and excited state by introducing an additional pump beam prior to a DFWM-sequence (Pump-DFWM). Via phase modulation of this initial pump pulse, coherent control is extended to structural evolution on the vibrationally hot ground state (hot-S 0 ) and lowest lying excited state (S 1 ) of β-carotene. In an open loop setup, the control scenarios for these different electronic states are compared in their effectiveness and mechanism.

A framework for calculating the intensity distribution and vibrational fine structure in the polarized ligand-field spectrum of transition metal complexes using the Herzberg-Teller approach is introduced and used to model the spectrum of the [PtCl4]2- ion. The model uses geometries, vibrational frequencies, and transition moments generated using density functional calculations on the ground and excited states, which arise from spin-allowed reorganization of the d electrons. The model predicts the whole spectral trace, including the polarization, the difference in the frequency of the electronic origin, the band maximum and the vertical transition energy, and the temperature dependence of the band intensities and the frequencies of the band maxima. Excitation to the 1A2g state is accompanied by a vibrational progression in the breathing mode of the excited state, as observed experimentally. Excitation to both the 1B1g and 1Eg states is accompanied by a loss of planarity and extended vibrational progressions in two modes, and the resulting spectra are inherently of low resolution.

The energy spectrum of low-frequency vibrational modes in amorphous polyisobutylene doped with chromophore tetra-tert-butylterrylene molecules has been measured. The technique for measuring the spectra of vibrational modes in solid amorphous media by single-molecule spectroscopy is described. The measured spectrum is compared with the data on the density of vibrational states (bosonic peak) in pure polyisobutylene, which were obtained by inelastic neutron scattering. It is shown that incorporation of small amounts of tetra-tert-butylterrylene into polyisobutylene did not significantly change the low-temperature vibrational dynamics of the matrix.

A theoretical study of molecular, electronic, and vibrational properties of the first excited state of the phenoxyl radical, A 2B2, is presented. The calculated molecular geometries, vertical and adiabatic excitation energies, and harmonic vibrational frequencies are compared with analogous results obtained for the ground state. The calculated excitation energies correspond well to experimental data. The harmonic vibrational frequencies of the A 2B2 and the ground state are similar except for modes involving the vibrations of the CO bond.

Nonlinear vibrational spectroscopy by use of mid-infrared femtosecond pulses enables the observation of ultrafast vibrational/structural dynamics of molecular systems. This article presents the recent experimental studies on vibrational energy relaxations and energy transfer in liquid water. In pure liquid water, vibrational energy relaxation of OH-stretching and OH-bending excitation occurs at about 200fs and 170fs, respectively. When vibrational energy from individually excited water molecules is transferred to intermolecular modes, a sub-100fs nuclear rearrangement occurs, leaving the local hydrogen bonds weakened but unbroken. Subsequent energy delocalization over many molecules proceeds with the breaking of hydrogen bonds on an 1-ps time scales. The observed vibrational/structral response should be relevant for chemical reactions and structural changes in aqueous environments.

The phase transition effects in (NH4)3TiOF5 and Rb2KTiOF5 were studied by vibrational spectroscopy over a wide range of temperatures. Changes in the spectra of these crystals were found for a PT in the region of the internal vibrations of the [TiOF5]3− ion. Quantum-chemical simulation of the vibrational spectra of (NH4)3TiOF5 was performed, and band assignments were carried out. The structure of the compound and the mechanism of the structural phase transition were examined. It is shown that the vibrational spectra of the compounds at room temperature depend on the dynamic disordering of the complex anion.

Laser-induced grating spectroscopy is applied to measure weak overtone and combination bands of methane between 11 170 and 11 980 cm−1 at pressures ranging from 0.2 to 4 bar and ambient temperature. The background-free method yields rotationally resolved spectra of transitions exhibiting cross-sections as low as ≈ 10−26 cm2/molecule. The technique is suitable for clarifying the near-infrared spectra of planetary objects and to provide data for the development and verification of new models describing the complex energy structure of highly vibrationally excited molecules. Copyright © 2008 John Wiley & Sons, Ltd.

Previously we obtained self-broadened halfwidth and self-induced shift coefficients at room temperature for 15 near infrared CO 2 bands between 4750 and 7000 cm −1 [R.A. Toth, L.R. Brown, C.E. Miller, V.M. Devi, D.C. Benner, J. Mol. Spectrosc., 239 (2006) 243–271]. The present study expands our work on the near infrared line parameters of CO 2 to include air broadening coefficients. Here we report nearly 400 air-broadened half width and air-induced pressure shift coefficients spanning 11 different CO 2 vibrational bands in the 4750–7000 cm −1 region. Retrievals have been performed using Voigt line profiles over three distinct spectral intervals: (a) 4750–5200 cm −1 , covering the 20011 ← 00001, 20012 ← 00001, and 20013 ← 00001 Fermi Triad and three associated hot bands 21111 ← 01101, 21112 ← 01101, 21113 ← 01101; (b) 6100–7000 cm −1 , covering the 30011 ← 00001, 30012 ← 00001, 30013 ← 00001 and 30014 ← 00001 Fermi Tetrad; (c) near 6950 cm −1 for the 00031 ← 00001 overtone band. The air-broadened halfwidth and air-induced pressure shift coefficients have been modeled with empirical expressions and compared to other measurements available in the literature.

The molecular geometry, IR intensities, harmonic and anharmonic vibrational frequencies of 4-, 5-, 6-chloroindole in the ground state were calculated by DFIF/B3LYP level of theory using the 6-31G (d, p) basis set. To give complete and reasonable vibrational assignments, the normal coordinate analysis has been performed for 4-chloroindole, 5-chloroindole and 6-chloroindole. The effect of position of chloro atom on the molecular properties (electron density, dipole moments and energies) of the indole aromatic system is examined on the basis of calculation data for 4-, 5- and 6-chloroindoles.

The Morse function is invaluable for describing the vibrational motion of diatomic molecules. The time independent Schrodinger equation can be solved in closed form for this potential only if molecular rotation is ignored or if the rotation is isolated from the vibrational motion by approximating it as a rigid rotor. To find the dependence of the energy eigenvalues on the vibrational and rotational state to a level of approximation that includes vibrational-rotational coupling, a higher level of approximation than the rigid rotor model is required. We present a method that can be understood by undergraduates, thus making the Morse potential a more useful example. The method yields results that are identical to those presented by Morse, but in a more elementary way.

One hundred and ninety-nine spectral lines in the (9, 1) overtone band of the a 3 Π state of the CO molecule in the near infrared region of 12,350–12,850 cm −1 are observed by employing optical heterodyne and magnetic rotation enhanced concentration modulation spectroscopy for the first time due to the strong perturbation between the v = 9 of a 3 Π and v = 2 of d 3 Δ levels. Additionally, 680 lines in the (2, 1) band of CO a 3 Π–d 3 Δ system are observed. Therefore, the most accurate molecular constants of these two perturbed levels, together with their perturbation constants, are obtained by non-linear least squares fitting using effective Hamiltonians. Our results show the improvement of about one order.

We present experimental data on the previously unknown line broadening and shifting coefficients in the (2 ← 0) overtone vibration–rotation bands of the HBr and HI molecules in mixtures with several rare gases. The vibrational dependence of the isotropic and anisotropic components of the binary interaction potential is probed by separating the measured line shifts into parts symmetric and asymmetric in the line number m and by comparing with the previously published similar data for the fundamental bands of the same molecules. It is shown that the line shifts are dominated by the vibrational dependence of the isotropic potential. A linear correlation is found between the asymptotic values of the symmetric shifts in the overtone bands for all HX–Rg (X = F, Cl, Br, I) pairs and the respective C6 long-range potential energy constants. Line broadening parameters in the overtone band of pure HBr are also reported.

Infrared spectra of the NH stretching vibrations of (NH3)n clusters (n = 2−4) have been obtained using the helium droplet isolation technique and first principles electronic structure anharmonic calculations. The measured spectra exhibit well-resolved bands, which have been assigned to the ν1, ν3, and 2ν4 modes of the ammonia fragments in the clusters. The formation of a hydrogen bond in ammonia dimers leads to an increase of the infrared intensity by about a factor of 4. In the larger clusters the infrared intensity per hydrogen bond is close to that found in dimers and approaches the value in the NH3 crystal. The intensity of the 2ν4 overtone band in the trimer and tetramer increases by a factor of 10 relative to that in the monomer and dimer, and is comparable to the intensity of the ν1 and ν3 fundamental bands in larger clusters. This indicates the onset of the strong anharmonic coupling of the 2ν4 and ν1 modes in larger clusters. The experimental assignments are compared to the ones obtained from fir...

The vibrational structure of the fluorescence spectrum and the structure of a dinaphthylethylene molecule in an excited state are calculated in the first and second approximations of the parametric method employed in the theory of vibronic spectra. The calculated spectra are in quantitative agreement with experimental data. The role of the angular parameters of the parametric method in the quantitative prediction of the vibrational structure of the fluorescence spectrum and changes observed in the geometry of the dinaphthylethylene molecule under excitation is determined. It is demonstrated that the polyene and acene parameters of the parametric method possess a high degree of transferability and that the models obtained are quite adequate to the real structures of the molecules under investigation. The proposed approach permits qualitative predictions and quantitative predictive calculations of the spectra of the studied molecules, as well as the spectral characteristics necessary for simulation of photochemical molecular transformations.

The lowest frequency perpendicular fundamental band ν 9 of disilane has been analyzed to investigate torsion mediated vibrational interactions. We report here a three-band analysis involving torsional levels built on the ground state, the ν 9 vibrational fundamental, and ν 3 fundamental. This analysis includes transitions from the far-infrared torsional bands, ν 4 , 2 ν 4 − ν 4 , 3 ν 4 − 2 ν 4 , two perturbation-allowed rotational series from the overtone band 3 ν 4 and transitions restricted to −21 ⩽ k Δ k ⩽ 21 in the ν 9 fundamental band. An excellent fit to the included data was obtained. Two interactions are identified in this fit, a resonant Coriolis interaction between the ν 9 torsional stack and that of the ground vibrational state and a Fermi interaction between the ν 3 fundamental and the gs. The introduction of the Fermi interaction causes a large change in the barrier height for the ground vibrational state and makes the barrier shape parameter redundant, indicating that the vibrational contributions to the experimental barrier shape are dominant. Such effects have also been observed for ethane and other similar molecules.

The vibrational spectrum and ground electronic state potential energy surface (PES) of thiophosgene (CSCl 2 ) have been studied quantum mechanically using a completely symmetrized Hamiltonian formalism and vibrational basis set, including all six molecular vibrational modes in the calculations. The calculated vibrational frequencies have been compared to the experimentally measured data by other authors. From a good fit achieved between the theoretical and experimental frequencies up to considerably high excess vibrational energies, the harmonic and some anharmonic (cubic and quartic) force constants of the molecular PES have been reliably determined.

The high-resolution Fourier transform absorption spectrum of an isotopic sample of nitrogen dioxide, 15N16O2, was recorded in the 3.4 μm region. Starting from the results of a previous study [Y. Hamada, J. Mol. Struct. 242 (1991) 367–377] a new analysis of the ν1 + ν3 band located at 2858.7077 cm−1 has been performed. This new assignment concerns (1 0 1) energy levels involving rotational quantum numbers up to Ka = 10 and N = 54. Using a theoretical model which accounts for both the electron spin-rotation resonances within each vibrational state and the Coriolis interactions between the (1 2 0) and (1 0 1) vibrational states, the spin-rotation energy levels of the (1 0 1) vibrational state could be reproduced within their experimental uncertainty. In this way, the precise vibrational energy, rotational, spin-rotation, and coupling constants were achieved for the {(1 2 0), (1 0 1)} interacting states of 15N16O2. Using these parameters and the transition moment operator which was obtained for the main isotopic species, 14N16O2, a comprehensive list of the line positions and intensities was generated for the ν1 + ν3 band of 15N16O2.

A refined temperature model of CO2 lasers is presented, which takes into account the fact that vibrational modes of the CO2 molecule have the common ground vibrational level. New formulas for the occupation numbers and the vibrational energy storage in individual modes are obtained as well as expressions relating the vibrational temperatures of the CO2 molecules with the excitation and relaxation rates of lower vibrational levels of modes upon excitation of the CO2–N2–He mixture in an electric discharge. The character of dependences of the vibrational temperatures on the discharge current is discussed.

In this article we present the spectrum of H13C13CH near 13 000 cm−1 and its ro-vibrational analysis. Our high repetition rate cavity ringdown spectrometer was used to record the spectrum. Seven vibrational bands, including six to previously unobserved vibrational states, were recorded and rotationally analysed. The band origin of the cold 3010000 stretching vibrational combination transition ((31-) in the local mode notation) was measured at 12 960.28807(38) cm−1. The vibrational transition dipole moments were determined through intensity measurements of the spectral peaks. The values of the unperturbed vibrational transition dipole moment, , and the first Herman–Wallis coefficient, A 1, for the 3010000 band were found to be 1.1570(26)×10-9 D2 and -9.5(6)×10-4, respectively. The numbers in parentheses represent a one-standard error in the least significant digits.

Nitrogen-broadened water vapor line parameters of the (2 1 1) ← (0 0 0) overtone band transitions in the 818–834 nm wavelength region are measured by using a tunable diode laser spectrometer. Water vapor is kept at its saturated vapor pressure at room temperature within a sample cell. Use of a balanced detector and a lock-in amplifier helps to increase the detection efficiency and the signal-to-noise ratio. The collisional broadening coefficients are extracted from the fitting of the experimental data by using a standard Voigt line profile. Collisional half-widths of water vapor lines perturbed by nitrogen are evaluated using the complex-valued implementation of the Robert–Bonamy (CRB) formalism. The rotational wave functions and the energy eigenvalues in the (2 1 1) vibrational state of water molecule are assumed on the basis of symmetry properties. Hence the outcome of this work also tests the validity of the theoretical approximations. The experimental data are compared with the corresponding theoretical values and the possible causes of deviation between the two have also been discussed.

In this work, an overtone two-dimensional infrared (2D IR) method is shown to allow correlated molecular motions at the frequencies of overtone transitions to be studied. Waiting-time-dependent overtone 2D IR results of the C-O stretching in neat liquid methanol reveal that the autocorrelation of the v = 0 → 2 transition and the cross correlation of the v = 0 → 2/v = 2 → 4 transitions differ considerably (relaxation time being 700 fs and 2 ps, respectively), suggesting different spectral diffusion dynamics. Quantum-chemical computations in combination with ab initio molecular dynamics simulations show that the overtone transition frequency of the C-O stretching mode in liquid methanol is of more structural sensitivity than the fundamental frequency. This work demonstrates a new 2D IR approach to examining the structural sensitivities of the anharmonic potential parameters of higher vibrational states, which can be used to gain new insight into the ultrafast structural dynamics particularly for neat liquids.

Overtone (5ν1 and 6ν1) and combination (4ν1 + ν3 and 4ν1 + ν2) vibrational bands of gaseous HC3N, located in the visible range (14,600-15,800 and 17,400-18,600 cm(-1)), were investigated by cavity ring-down absorption spectroscopy. The 5ν1 + ν3 and 5ν1 + ν2 combinations as well as the 6ν1 + ν5 - ν5 hot overtone band have also been identified, on the basis of previous overtone assignments. Absolute integrated intensity values and the ensuing oscillator strengths have been measured here for the first time; f values are typically confined between 4 × 10(-12) and 7 × 10(-11). For the even weaker 5ν1 + ν2 combination band, the oscillator strength was estimated as 9 × 10(-13). The values concerning CH-stretch overtones (nν1) are similar to those found in the literature for HCN and C2H2, the molecules with sp-hybridized carbon atoms. Data presented here may prove useful for studying the photochemistry triggered with visible or near-IR radiation within the atmospheres of certain Solar System bodies, including Titan.

Shock tube experiments are carried out to study the physical and chemical processes during a vehicle entry into the Mars atmosphere using optical emission spectroscopy and tunable diode laser absorption spectroscopy . Gas temperature and CO concentration distribution are diagnosed behind a shock wave in a CO2-N-2 mixture with two different conditions of initial pressure and velocity. The strong shock wave is established in a shock tube driven by combustion of hydrogen and oxygen. Time-resolved spectra of the Delta v = 0 sequence of the B-2 Sigma-g X-2 Sigma electronic transition of CN have been observed through OES. A precise analysis of the CN violet spectra is performed and used to determine rotational and vibrational temperatures. Two absorption lines in the first overtone band of CO near 2.33 mu m are selected from a HITRAN simulation to calibrate laser wavelength and detect the CO concentration. Combined with these temperature results using OES CO concentrations in the thermal equilibrium region are derived which are 2.91 x 10 cm and 1.01 x 10 cm corresponding to equilibrium temperatures equal to 7000 +/- 400 K and 6000 +/- 300 K in low and high pressure conditions respectively.

Vibrational energy flow in the electronic ground state of photoactive yellow protein (PYP) is studied by ultrafast infrared (IR) pump-visible probe spectroscopy. Vibrational modes of the chromophore and the surrounding protein are excited with a femtosecond IR pump pulse, and the subsequent vibrational dynamics in the chromophore are selectively probed with a visible probe pulse through changes in the absorption spectrum of the chromophore. We thus obtain the vibrational energy flow with four characteristic time constants. The vibrational excitation with an IR pulse at 1340, 1420, 1500, or 1670 cm(-1) results in ultrafast intramolecular vibrational redistribution (IVR) with a time constant of 0.2 ps. The vibrational modes excited through the IVR process relax to the initial ground state with a time constant of 6-8 ps in parallel with vibrational cooling with a time constant of 14 ps. In addition, upon excitation with an IR pulse at 1670 cm(-1), we observe the energy flow from the protein backbone to the chromophore that occurs with a time constant of 4.2 ps.

We studied the effects of hydrogen bonds on the vibrational structures and vibrational dynamics of the CO stretching mode of 9-fluorenone (FL) in the electronically excited state in aprotic and protic solvents using sub-picosecond visible-pump and IR-probe spectroscopy. The transient IR spectrum of the CO stretching band in methanol-d4 has two bands at 1529.9 cm−1 and 1543.4 cm−1, which are assigned to an FL-solvent complex and free FL, respectively. In the aprotic solvents, the CO stretching bands show blue-shifts in time. This shift is due to vibrational cooling, which is derived from anharmonic couplings with some low-frequency modes. Interestingly, a red-shift is observed at later delay time for the band at 1529.9 cm−1 in methanol-d4. A possible mechanism of this spectral shift is related to the hydrogen bond dynamics between the solute and solvent.

It is demonstrated how vibrational IR and Raman spectra can be calculated from damped response functions using anharmonic vibrational wave function calculations, without determining the potentially very many eigenstates of the system. We present an implementation for vibrational configuration interaction and vibrational coupled cluster, and describe how the complex equations can be solved using iterative techniques employing only real trial vectors and real matrix-vector transformations. Using this algorithm, arbitrary frequency intervals can be scanned independent of the number of excited states. Sample calculations are presented for the IR-spectrum of water, Raman spectra of pyridine and a pyridine-silver complex, as well as for the infra-red spectrum of oxazole, and vibrational corrections to the polarizability of formaldehyde.

The v 1 +v 2 +v 3 absorption band of the SO2 molecule is recorded and analyzed for the first time on the basis of the specially developed procedure for assignment of superweak high-resolution spectra. The spectral line positions obtained from an analysis of the experimental spectrum are used for the determination of rotational and centrifugal distortion parameters of the (111) state.

A time–domain method for calculating two-dimensional infrared (2D-IR) spectra is developed and is applied to the case of the amide I band of liquid N , N -dimethylformamide. This method includes the effects of both the diagonal frequency modulations (of individual molecules in the system) and the off-diagonal (intermolecular) vibrational coupling. The effect of the off-diagonal vibrational coupling on the 2D-IR band profiles is examined. The band profiles for three types of 2D-IR optical processes are compared and discussed in relation to this effect.

We form ultracold ground-state Rb2 molecules by photoassociating pairs of atoms in a magneto-optical trap into the 0u+ state, which decays radiatively into high vibrational levels of the X1Σg+ state. Sensitive and vibrationally state-selective detection is achieved by means of resonantly-enhanced two-photon ionization with a pulsed laser. Frequency scans of the detection laser reveal a long vibrational progression to a previously unobserved electronic excited state, which we identify as the 21Σu+ state. Most of its vibrational spectrum is in excellent agreement with predictions based on ab initio potentials, although the lowest vibrational levels exhibit strong perturbative mixing with the triplet 23Πu state. The detection method reported here, with minor variations, should be effective for the entire potential well of the X state. In this work no transitions are observed from vibrational levels above v = 118, but this turns out to be a limitation not of the detection method but rather of the photoassociative formation scheme, due to re-excitation of the highest-v levels by the same photoassociation laser that produces them.

We show that the de-excitation to different vibrational levels of the ground state in NaH molecule can be controlled by using two delayed ultrashort pulses (4 fs Gaussian). A vibrational wave packet generated on the excited A1Σ+ state by the first pulse is de-excited back to the ground state by a second pulse after a time delay. The cross-section for de-excitation of the wave packet to different vibrational levels of the ground electronic state can be controlled by controlling the delay time between the two pulses as well as by choosing a pulse duration much shorter than the vibrational period of the molecule, such that the de-excited wave packet remains localized in the Franck–Condon region of a particular vibrational level of the ground state. Hence, the de-excitation to a particular vibrational level can be enhanced by suppressing that in others. In spite of the large bandwidth of the pulse which includes nine vibrational levels of the upper state and five vibrational levels of the ground state, one ca...