Experimental and theoretical investigation of the photoionization of hydrogen cyanide

Cryogenic matrices containing molecular aggregates of methyl nitrite or methanol have been irradiated with a cw CO₂ laser. At the irradiation frequency hole burning was observed by means of a grating infrared spectrophotometer. The results suggest that vibrational absorption lineshapes of aggregates in cryogenic matrices are dominated by inhomogeneous line-broadening.     

FTIR and Raman studies on benzimidazole

The FTIR and laser Raman spectra of benzimidazole have been recorded. The observed frequencies were assigned to various modes of vibrations on the basis of normal coordinate calculations, assuming C_s point group symmetry. The potential energy distribution associated with normal modes is also reported here. The assignment of fundamental vibrations agrees well with the calculated frequencies.     

Raman and i.r. spectra of tetramethylcyclobutanedione and the fully deuterated derivative

Raman spectra of tetramethylcyclobutane-1,3-dione (TMCBD) as a polycrystalline solid and in solution in benzene and carbon tetrachloride have been recorded. Infrared and Raman spectra of the fully deuterated molecule have also been recorded. The spectra are consistent with predictions based on a centrosymmetric molecule with a planar cyclobutadione ring and point group D_2h. A fairly complete assignment of the observed spectra is presented for both molecules. A correlation of the frequencies of the fundamentals of TMCBD-h₁₂ and - d₁₂ has been made. Ground state frequencies of fundamentals involved in progressions in the n-π* electronic spectrum have been located.     

Infrared and electronic absorption spectra of some trisubstituted benzenes

The electronic absorption spectra of 2,3-, 2,4-, 2,5-, 2,6- and 3,4-difluorobenzonitriles, 3,4-difluoroaniline and 3,4-difluoroanisole in the ultraviolet region in vapour phase have been recorded on medium quartz and Hilger large quartz spectrographs and on a Hitachi model 150-20 UV-VIS ratio recording spectrophotometer. All the molecules investigated have exhibited two π* ← π band systems corresponding to ¹B_2u ← ¹A_1g (λ2600 Å) and ¹B_1u ← ¹A_1g (λ2100 Å) systems of benzene. The infrared absorption spectra of all the molecules studied have also been recorded and analysed. These infrared data have been taken to help analyse the u.v. spectra of the molecules studied.     

The appearance of fine structure in the phosphorescence spectra of organic molecules in solid solutions under T1 ← S0 laser excitation

Phosphorescence spectra of coronene. 1,2-benzypyrene and chrysene in bromobutyl at 4.2 K under laser excitation directly in the region of the T₁ ← S₀ transition have been studied. Under these conditions, the phosphorescence spectra acquire a line structure. Vibrational analysis of the spectra has been performed and the frequencies of the normal vibrations of the investigated molecules in the S₀ state have been determined. A “multiplet” structure of the phosphorescence spectra appearing for monochromatic excitation to vibrational sublevels of the T₁ state has been studied. It is shown that the frequencies of the molecular vibrations in a triplet state can be found from an analysis of this structure.     

Laser Raman and IR spectra and force fields for 2,6-difluorobenzonitrile

Raman spectrum of 2,6-difluorobenzonitrile in the powder form has been recorded in the region 50–4000 cm⁻¹ on a Jasco K-500 spectrophotometer using the 488.0 nm radiation from an argon laser. IR spectra in the region 200–4000 cm⁻¹ have been recorded in KBr pellet and nujol mull on a Nicolet DX spectrometer and in liquid and vapour phases on a Jasco FTIR/7000 spectrometer. Using these observed frequencies force field calculations for the planar and non-planar modes have been carried out assuming a general valence force field.     

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.     

Microwave and infrared spectra of deuterium-substituted germyl halides and the structures of the germyl halides

We have obtained microwave spectra of fully and partially deuterated germyl halides GeD₃X and GeHD₂X (X = F, Cl, Br, I) and analysed the infrared spectra in the GeH stretching region of the asymmetric species. The resulting A_o and B_o values have been combined with existing data on GeH₃X to give improved structures for the germyl halides. The values of the HGeX angles obtained show a correlation with GeH stretching frequencies, as in methyl compounds, but there appears to be no such correlation between stretching frequencies and GeH bond lengths.     

Infrared-microwave double resonance study of the ν4 fundamental band of POF3

Three-level and four-level infrared-microwave double resonance effects have been observed in a POF₃ sample contained in a microwave waveguide Stark cell that was modified to permit transmission of radiation from a CO₂ infrared gas laser. In three-level double resonance experiments laser pumping of rotational states in the ν₄ = 1 vibrational state greatly increased the signal/noise for observation of Stark-shifted rotational transitions in the excited vibrational state. The frequencies of the observed excited state transitions were used to confirm the assignment of laser Stark spectra and to obtain independent measures of the rotational constant B and the dipole moment for ν₄ = 1. The observation of four level double resonances could be explained qualitatively by the assumption of dipole selection rules for collision-induced transitions. However, the intensities of the double-resonance effects could not be explained by this simple model.     

Infrared studies in the ν1 of ONCI: CO laser line coincidences and pressure broadening data

46 Spectral quasi-coincidences between CO laser lines and ClNO absorption lines are given. The ONCl ν₁ spectra have been obtained using a Fourier transform spectrometer. In four cases the discrepancies between the frequencies are smaller than the Doppler width. Pressure broadening parameters resulting from collisional perturbations by Ar for two rotational transitions in the ν₁ band of ONCl have been measured using a diode laser spectrometer.     

Vibrational spectra of the trans-trans and trans-cis conformers of dimethyl fumarate

Infrared and Raman spectra of dimethyl fumarate (DMFU) have been recorded in the temperature range 12–390 K. The solid state spectra are consistent with the trans-trans conformation. However, in the liquid phase (melt or solution in CCl₄) and in the vapour phase, additional infrared and Raman bands were observed due to the presence of the trans-cis conformer. For the trans-trans conformer the observed spectra have been assigned on the basis of a C_2h molecular symmetry. A normal coordinate analysis of trans-trans DMFU has been carried out using a modified Urey- Bradley force field to assist in the assignment. Observed frequencies for the trans-cis conformer have been assigned on the basis of a structure of C_s symmetry.     

Raman and infrared studies of NaLa(MoO4)2:Nd3+

The polarized Raman and i.r. (powder) spectra of 0.5 mole % neodymium doped NaLa(MoO₄)₂ have been analysed on the basis of C_4h crystal symmetry. Group theoretically predicted fundamentals have been observed. The frequencies and intensities are not altered due to doping.     

Fourier Spectrometer based on Wide-range and Phase-locked Michelson Interferometer with Femtosecond Laser Excitation

A wide-range and phase-locked Michelson interferometer technique is described.This technique combined with femtosecond laser is used to measure the spectrum of the rare-earth ion Nd:YVO₄, which presents very high signal to noise ratio of interferometric intensity output and higher spectral resolution than traditional grating spectrophotometer.     

Spectra and structure of phosphorus—boron compounds—XXVI. Infrared and Raman spectra,conformational stability and normal coordinate analysis of ethyldichlorophosphine-borane

The Raman (3500-10 cm⁻¹) and infrared (3500-50 cm⁻¹) spectra of solid ethyldichlorophosphine-borane, CH₃CH₂P(BH₃)Cl₂ and its deuterated analog, CH₃CH₂P(BD₃)Cl₂ have been recorded. Additionally, the infrared spectra of the gases and the Raman spectra of the liquids have been recorded and qualitative depolarization ratios have been obtained. Based on the fact that several distinct Raman lines disappear on going from the liquid to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers, with the trans conformer being more stable in the liquid phase, and the only one present in the solid phase. From a temperature study of the Raman spectrum of the liquid, the enthalpy difference between the gauche and trans conformers was determined to be nearly zero. Based on Raman depolarization data, group frequencies, isotopic shift factors and infrared band contours, a complete vibrational assignment has been proposed for the trans conformer. The assignment is supported by a normal coordinate calculation which was carried out utilizing a modified valence force field to obtain the frequencies of the normal modes and the potential energy distribution. The BH₃ torsion has been observed at 188 cm⁻¹, while the BD₃ torsion was not observed. The methyl torsions in the spectra of the solids have been observed at 209 and 202 cm⁻¹ for the “light” and deuterated species, respectively. From the torsional data, barriers to internal rotation have been calculated. The asymmetric torsional mode has been observed for the trans conformer in the infrared spectra of the gas phase at 108 and 104 cm⁻¹ for the BH₃ and BD₃ species, respectively. These results are compared with similar quantities for some corresponding organophosphine—borane compounds.     

Spectroscopic investigations of phase transition in 5-chloro-2-pyridone

Spectroscopic investigation of 5-chloro-2-pyridone has been carried out in the temperature range 77–300 K. At room temperature the ³⁵Cl NQR spectrum shows a single line at 35.618 MHz, but at 250.7 K two lines appear at 35.850 MHz and 35.840 MHz respectively indicating the presence of a phase transition. IR, far-IR, laser Raman and dielectric measurements have been carried out to investigate the phase transition further. Low temperature IR studies show splitting of ν(CCl), β(NH) and ν(CO) bands at T_c. Dielectric measurements show a small, but finite, change in the value of the dielectric constant around T_c. Raman spectra at different temperatures support the existence of a new phase, as shown by the appearance of a new band at 81 cm⁻¹, the frequency of which changes slowly as T_c is approached and which disappears at T_c. The temperature dependence of the NQR frequencies has been analysed using Bayer Kushida and Brown equations toevaluate the torsional frequencies.     

Characterization of the vibrational behaviour of a bridge with the coordination number 2: III. The case of nonequivalent bridge bonds

Thirty-one complexes with general formula trans- [Co(NO₂)(AA)₂B] (where AA represents the acetylacetonate anion and B represents a range of variously substituted anilines or pyridines) have been synthesized and their infrared spectra determined. ¹⁵N-labelling of the complexes in which B is aniline and p-toluidine yields assignments of the cobalt-amine stretching frequencies and the internal vibrations of the amino group. Assignments of the cobalt-oxygen and cobalt-nitro stretching frequencies are based on comparison of the spectra with those of [Co(AA)₃] and trans-Na[Co-(NO₂)₂(AA)₂]. The assignments are supported by the nature of the dependence of the frequencies on the electronic effects of the substituents in the aniline and pyridine rings.     

Vibrational spectra and structure of the photochromic 2-(2′,4′-dinitrobenzyl)pyridine

The molecular structure of the pale yellow crystals of 2-(2′,4′-dinitrobenzyl)pyridine (CH₂ form) and its photo induced ‘enamine’ NH tautomer (dark blue crystals) have been studied by means of vibrational spectra and ab initio calculations. The Raman spectrum of the photo-sensitive CH₂ form was registered by NIR FT-Raman spectroscopy by means of the Nd:YAG laser as an excitation source. Ab initio calculations have been performed for the CH₂ and NH tautomers at the Hartree-Fock level using a 6-21G** basis set. The theoretical geometrical parameters for the isolated 2-(2′,4′-dinitrobenzyl)pyridine molecule (CH₂ form) are close to the literature X-ray diffraction data. According to the theory the dihedral angle between the benzene and pyridine ring planes in the NH photo induced tautomer is about 46°, the ortho-nitro group is twisted about 25° towards the benzene ring plane, whereas the para-nitro group is coplanar to the benzene ring. The assignment of the fundamental vibration frequencies of both 2-(2′,4′-dinitrobenzyl)pyridine tautomers CH₂ and NH have been performed on the basis of Raman and infrared spectra and ab initio force field calculations. The computed frequencies are in coincidence with the registered ones; the mean deviations are between 23.7 and 28.5 cm⁻¹.     

Infrared,Raman and NMR spectra,conformational stability,and ab initio calculations of divinylmethoxyborane

The infrared spectra (4000–50 cm⁻¹) of gaseous and solid divinylmethoxyborane, (CH₂=CH)₂BOCH₃, as well as the Raman spectra (3500–20 cm⁻¹) of the liquid and solid have been recorded. Qualitative depolarization values have been obtained from the Raman spectrum of the liquid. All normal modes, except the torsions, have been assigned based on infrared band contours, depolarization values, group frequencies, and normal coordinate calculations. From a comparison of the spectra in the fluid and solid states, it is concluded that the molecule exists predominantly in a single conformation in all physical states. Frequencies and potential energy distributions for the normal modes have been calculated with the 3–21G basis set. A comparison of these calculated frequencies to the observed spectra is consistent with the predominant form having a “planar” heavy atom skeleton with C_s, symmetry. From the variable low temperature ¹³C NMR data, a barrier to rotation about the B-O bond of 10.1 ± 0.1 kcal mol⁻¹ has been determined, which is in excellent agreement with a barrier of 8.5 kcal mol"1 obtained from ab initio calculations. Structural parameters, conformational stability, and barriers to internal rotation have been obtained from ab initio Hartree-Fock gradient calculations employing both the 3–21G and 6–31G^* basis sets. The results are compared to the corresponding data for some similar organoboranes.     

Theoretical anharmonic Raman and infrared spectra with vibrational assignments for monofluoroaniline isomers

The ortho-meta-, and para-fluoro substituted anilines are prototype molecules for investigation of the interactions of both the amino group and the fluorine atom with the aromatic ring. The molecular structures, natural atomic charges and theoretical anharmonic Raman and infrared spectra of the three fluoroaniline isomers have been calculated by using the density functional B3LYP method with the extended 6-311++G(df,pd) basis set. The Raman and infrared spectra of 2FA, 3FA, and 4FA have been recorded. The detailed vibrational assignments of the experimental spectra have been made on the basis of the calculated potential energy distributions, PEDs. The effect of fluorine substituent on the aniline ring geometry and charge distribution, the nature of the characteristic “marker bands” and a quenching of intensities of some bands are discussed. It is shown that the frequencies of the NH₂ stretching vibrations depend on the degree of pyramidalization of the C-NH₂ group, in the isomers. In 2FA and 3FA, the NH₂ stretching frequencies are higher than those in 4FA. This corresponds to a more flattened structure of the amino group in 2FA and 3FA, in comparison to 4FA.     

Vibrational spectra and structure of cyclopropane-d1 and dicyclopropyl ketone

Infrared spectra have been obtained for cyclopropane-d₁, C₃H₅D(CP-d₁), in the vapor phase and for dicyclopropyl ketone (C₃H₅)₂ CO (DCPK) in the liquid state. Raman spectra of the latter compound in the liquid and solid phases have also been recorded. By comparing the experimental with the theoretical spectra of CP-d₁ it has been possible to assign most of the fundamental frequencies of the molecule. Additionably, empirical spectra—structure correlations from the literature for cyclopropyl derivatives containing the COX moiety (X=halogen) have been used to investigate the conformational preference of DCPK. The experimental results confirm that the molecular configuration with the carbonyl group cis to the planes of the two rings is the predominant species in the liquid state, though evidence for a second conformer, which we tentatively identify as the cis—trans conformer, is presented.