Hydrogen-bonded OH stretching modes of methanol clusters: a combined IR and Raman isotopomer study

A comprehensive study of the OH and OD stretching fundamentals in clusters of methanol and its isotopomers CH(3)OD, CD(3)OH, and CD(3)OD provides detailed insights into the hydrogen-bond mediated coupling as a function of cluster size. The combination of infrared and Raman supersonic jet spectroscopy enables the observation and assignment of all hydrogen-bonded OH stretching modes of isolated methanol trimer and methanol tetramer. A consistent explanation for the spectral complexity observed more than a decade ago in methanol trimer in terms of low-frequency methyl umbrella motions is provided. Previous explanations based on cluster isomerism or anharmonic resonances are ruled out by dedicated jet experiments. The first experimental lower bound for concerted quadruple proton transfer in S(4) symmetric methanol tetramer is derived and compared with theoretical predictions. The observed isotope effects offer insights into the anharmonicity of the localized OH bond. The performance of harmonic B3LYP and MP2 calculations in predicting hydrogen-bond-induced spectral shifts and couplings is investigated.     

The photoelectron spectra of the OH and OD radicals

He(I) photoelectron spectra of the hydroxyl radical show ionizations corresponding to the production of OH⁺ (OD⁺) in the states X ³Σ^? and ¹Δ at ionization potentials of 13.01 eV and 15.20 eV respectively. The excitation energy of the ¹Δ state is in very good agreement with that predicted by calculation and experiment; vibrational spacings in the X ³Σ^? state agree with emission spectroscopic data.     

Theoretical modeling of infrared spectra of benzoic acid and its deuterated derivative

Theoretical simulation of the ν_s stretching band is presented for benzoic acid and its OD derivative at 300 K. The simulation takes into account an adiabatic coupling between the high-frequency O–H(D) stretching and the low-frequency intermolecular OO stretching modes, linear and quadratic distortions of the potential energy for the low-frequency vibrations in the excited state of the O–H(D) stretching vibration, resonance interaction between the two hydrogen bonds in the dimer, and Fermi resonance between the fundamental ν OH(D) stretching and the overtone of the δ O–H(D) bending vibrations.

Infrared, far-infarared, Raman and low-frequency Raman spectra of the polycrystalline benzoic acid and its deuterated form have been measured. The geometry and experimental frequencies are compared with the results of our B3LYP/6-311++G** and B3LYP/cc-pVTZ calculations.     

Transverse and longitudinal crystal modes associated with OH stretching vibrations in single crystals of kaolinite and dickite

Raman spectra of randomly-oriented kaolinite, dickite and nacrite show, for coarsely crystalline material, an extra band in the OH stretching region which is absent from the IR spectra of clay-size samples. Oriented single-crystal Raman spectra of these minerals provide confirmation for the assignment of the extra bands to transverse optical modes involving in-phase coupled vibrations of the layer-surface hydroxyl groups. The corresponding IR bands have transition moments nearly perpendicular to the layer surface, and appear at the higher frequencies of the longitudinal optical modes of macroscopic crystals.     

High pressure Raman spectra of l-glutamic acid hydrochloride crystal

Semiorganic nonlinear optical single crystal l-glutamic acid hydrochloride has been studied by Raman spectroscopy under high pressure conditions. Our results show that this amino acid crystal presents one structural phase transition at about 2.1 GPa and one molecular conformational change around 7.5 GPa. If we compare such behavior with that of the l-glutamic acid crystal in the same range of pressure we note a great stability for the hydrochloride samples. The chloride ion plays an important role increasing the number of the hydrogen bonds that hold the crystal together and thus, contributing to improve the structural stability of the crystal.     

Time-domain calculations of the polarized Raman spectra, the transient infrared absorption anisotropy, and the extent of delocalization of the OH stretching mode of liquid water

The polarized Raman spectrum and the time dependence of the transient infrared (TRIR) absorption anisotropy are calculated for the OH stretching mode of liquid water (neat liquid H2O) by using time-domain formulations, which include the effects of both the diagonal frequency modulations (of individual oscillators) induced by the interactions between the dipole derivatives and the intermolecular electric field, and the off-diagonal (intermolecular) vibrational coupling described by the transition dipole coupling (TDC) mechanism. The IR spectrum of neat liquid H2O and the TRIR anisotropy of a liquid mixture of H2O/HDO/D2O are also calculated. It is shown that the calculated features of these optical signals, including the temperature dependence of the polarized Raman and IR spectra, are in reasonable agreement with the experimental results, indicating that the frequency separation between the isotropic and anisotropic components of the polarized Raman spectrum and the rapid decay (approximately 0.1 ps) of the TRIR anisotropy of the OH stretching mode of neat liquid H2O are mainly controlled by the resonant intermolecular vibrational coupling described by the TDC mechanism. Comparing with the time evolution of vibrational excitations, it is suggested that the TRIR anisotropy decays in the time needed for the initially localized vibrational excitations to delocalize over a few oscillators. It is also shown that the enhancement of the dipole derivatives by the interactions with surrounding molecules is an important factor in generating the spectral profiles of the OH stretching Raman band. The time-domain behavior of the molecular motions that affect the spectroscopic features is discussed.     

Density of vibrational states in trans-polyene: comparison with the infrared,Raman and neutron spectra of trans-polyacetylene

The density of states has been calculated for the in-plane and out-of-plane vibrations in the infinite trans polyene chains. Comparison of the density of states spectra with the IR and Raman spectra of trans-polyacetylenes, (CH)_x, (¹³CH)_x and (CD)_x, shows that most of the weak bands as well as the strong bands arise from the trans polyene segments in the polymer films. The IR bands newly assigned to the trans segments include the 740 cm⁻¹ band, which was previously assigned to remnant cis CC bonds. The IR spectra of (¹³CH)_x and (CD)_x clearly indicate that the amount of remnant cis bonds in thermally isomerized trans films is much smaller than that proposed previously. The hydrogen-amplitude-weighted density of states calculated for the infinite polyene chain also shows satisfactory agreement with a neutron inelastic scattering spectrum of trans-(CH)_x.     

The infrared spectra of trifluoromethanesulphonic acid in different states of aggregation

The infrared spectra of CF₃SO₃H in the gaseous, liquid and solid states, as well as dispersed in a solid Ar matrix, were obtained and analyzed. Association through H-bonds is demonstrated in all phases by a broad OH stretching band. Heating of the gas generates new bands due to the monomer, whereas freezing of the liquid causes a slight shift of the ν_OH band to higher frequencies and a drastic decrease in the intensity of the SO₂, deformation band, suggesting a large redistribution of the H-bonds.     

Polarized infrared and Raman spectra of a CsHSO4 single crystal

The polarized absorption infrared (IR) and polarized Raman spectra of a CsHSO₄ single crystal at room temperature are presented and discussed in relation to the X-ray crystal structure. Breakdown of the selection rules for the X-ray determined C_2h factor group is observed. The vibrational factor group appears to be C₂. This implies C₁ site symmetry for the SO²⁻₄ ions. The polarization features of the HSO⁻₄ ion vibrations are predicted assuming that the longest S---OH bond vibrates independently of the SO₃ group vibrations. The ABC structure of the IR and Raman band arising from the νOH stretching vibration is explained on the basis of Fermi resonance.     

Raman and infrared spectra of crystalline fluoroform

Raman and far-infrared spectra of crystalline fluoroform at temperatures between 20 and 106 K have been recorded. There is no evidence for any solid-state phase transitions, nor for hydrogen bonding. The rich lattice spectra and crystal field splittings suggest that the unit cell is rather large, and possible structures are discussed.     

Raman and infrared spectra of crystalline chloroform

Raman and far-infrared spectra of polycrystalline samples of chloroform at 20 and 80 K are reported. Crystal field spilttings of the intramolecular fundamentals are observed as well as nine Raman and six infrared lattice modes. Spectra are interpreted in terms of a group theoretical analysis based on the molecular and crystal symmetries.     

Raman and infrared spectra of lanthanum molybdate

The infrared and Raman spectra of gel-grown lanthanum molybdate were recorded. Group theoretical analysis was carried out and a vibrational assignment proposed based on C_2h symmetry. Factor group and site effects are discussed.     

Fluorescence-dip IR spectra of jet-cooled benzoic acid dimer in its ground and first excited singlet states

The IR spectra of three isotopomers of the benzoic acid dimer have been recorded under jet-cooled conditions using the double resonance method of fluorescence-dip IR spectroscopy. In so doing, the spectra are assuredly due exclusively to dimers in the ground-state zero-point level at a rotational temperature of 3-5 K. Even under these conditions, the three isotopomers have remarkably broad spectra, extending from 2600 to almost 3150 cm-1. The spectra show extensive substructure consisting of some 15-20 transitions where only a single OH stretch fundamental should appear in the harmonic limit. The comparison of the undeuterated d0-d0 dimer with the ring-deuterated d5-d5 dimer tests the effect of mixing with the C-H stretches and overtones of the C-H bends. The mixed OH/OD ring-deuterated d6-d5 dimer shifts the frequency and changes the form of the OH stretch normal mode. The analogous OH stretch IR spectrum of the d0-d0 dimer out of the S1 excited-state zero-point level has also been recorded. In this case, much of the closely-spaced substructure is not apparent. What remains is a set of three bands separated from one another by about 180 cm-1. Preliminary results of model calculations of the anharmonic coupling, responsible for the broadening and substructure, are presented. These calculations indicate that it is OH stretch-OH bend coupling, rather than coupling with the intermolecular stretch, that is responsible for much of the observed structure and breadth.     

Laser Raman and infrared spectra of deuterated silylgermanes

The laser Raman and infrared spectra of deuterated silylgermanes have been recorded on a Cary model 82 grating spectrophotometer with an argon laser source and a Perkin—Elmer 983 double beam grating spectrophotometer, respectively. The spectra have been analysed on the basis of fundamental combinations and overtones and the frequencies have been assigned to various modes of vibration, assuming C_3υ point group symmetry. Furthermore, based on the force field for silylgermanes, the vibrational frequencies of isotopically substituted species have been calculated and the results are briefly discussed.     

The infrared and Raman spectra of guanidinium salts

The i.r. and Raman spectra of guanidinium chloride, guanidinium perchlorate, and the deuterated derivatives of these salts, have been determined as solids and in solutions.     

The infrared and Raman spectra of pyromellitic dianhydride

The infrared and Raman spectra of solid state samples of pyromellitic dianhydride have been measured. The infrared—Raman mutual exclusion rule has been observed and the frequencies have been tentatively assigned on the basis of D_2h symmetry. The values of the CO and skeletal ring stretching frequencies have been interpreted in terms of a conjugated π-system.     

The infrared and Raman spectra of carbonyl diisocyanate

The infrared and Raman spectra of carbonyl diisocyanate have been recorded. Vibrational assignments have been made on the basis that two planar conformations are present both in the liquid and vapour phases: cis—cis and cis—trans. Simple normal coordinate calculations have been used to confirm the assignments.