The vibrational spectrum and normal coordinate analysis of chlorodifluoromethane,CHClF2

The vibrational spectrum of chlorodifluoromethane has been reexamined. The i.r. and Raman spectra of the three isotopic species, ¹²CHClF₂, ¹³CHClF₂ and ¹²CDClF₂, have been obtained with better accuracy and higher resolution than in previous work. An SCF ab initio geometry optimization and quadratic force field calculation have been performed, and this force field has been further optimized to best fit the observed frequencies. The absorption spectrum of the ν₄, 2ν₆ region has been recorded at high resolution (0.002 cm⁻¹) and an analysis of the Fermi resonance perturbation has been carried out.     

Time resolved fluorescence of anthracene in mixed crystals at 2K

An optical Kerr shuttered spectrograph has been used to time resolve the spontaneous fluorescence of aromatic mixed crystal systems at low temperature with moderate resolution. Transient effects on the fluorescence of anthracene in naphthalene excited with 614 cm^?1 vibrational excess energy in ¹B_2u have been observed that may signal measurable vibrational relaxation pathways. A model consistent with these observations is presented: it implicates a strong interaction between the intramolecular Franck—Condon and non-Franck—Condon modes in the relaxation process for specific excitation in the region of large excess lattice energy. Examination of the fluorescence for several aromatic systems integrated over the interval 0 to 30 ps following excitation high in the S₁ vibrational manifold failed to reveal evidence of non-Boltzmann vibrational distributions, although other largely unexplained effects have been observed.     

The 2B1 ← 2A1 system of nitrogen dioxide

The vibrational structure of the ²B₁ ← ²A₁ system of NO₂ has been assigned to a progression in ν′₂. Vibrational analyses for three isotopic species have been made using a hamiltonian which allows explicitly for a large-amplitude bending vibration. The system origin for the normal isotopic species has been assigned an extrapolated value of 14743.5 cm^?1. The bending potential function is expressed as a rapidly converging Taylor series expansion about the linear configuration. There is no evidence that the equilibrium configuration is nonlinear.     

Laser induced fluorescence of Sb2. I. Visible B–X system

Diatomic antimony molecules have been produced in a heat-pipe oven at pressures from 10^?2 to 10 Torr. Laser induced fluorescence of Sb₂ has been studied in the spectral range 420–730 nm with various laser sources. In order to investigate different isotopic molecules and to enhance fluorescence intensity, intracavity measurements have been performed. For the isotopic molecules rotational and vibrational constants of the ground state X(¹Σ_g⁺) and for the excited state B(O_u⁺) have been determined. RKR potential curves have been calculated and used to comput Franck—Condon factors.     

Structural and spectral consequences of ion pairing II. a theoretical study of CIO−3Li+ and ClO−3Na+

The structure of ClO⁻₃M⁺ ion pairs (M = Li, Na) has been examined with the aid of ab initio molecular orbital calculations. The calculations support recent experimental findings that ClO⁻₃ M ion paris have C_3v rather than C_s configurations. Results from these studies also show that the metal cation prefers to coordinate at the base of the chlorate anion pyramidal structure along the C₃ axis. Calculated vibrational frequencies, intensities, isotopic frequency shifts, and isotopic substituted frequency and intensity patterns render support to this conclusion. New vibrational assignments of observed and some unassignable bands from previous matrix-isolation and molten gas phase spectroscopic studies of ClO⁻₃M⁺ ion pairs are provided.     

Gas phase i.r. spectrum and vibro-rotational analysis of CH2BrCl

The gas phase i.r. spectrum of CH₂BrCl with natural isotopic abundance has been measured under medium resolution in the range 4000-350 cm⁻¹. Accurate inspection of the band contours enabled us to positively identify most of the observed absorptions including fundamentals, overtones and combinations. The frequency value of the lowest fundamental ν₆, lying below the spectral range examined, has been evaluated by difference of suitable combinations and “hot” bands. B- and C-type absorptions exhibiting resolved rotational structure have been analyzed in terms of perpendicular bands in the symmetric rotor approximation and molecular parameters have been deduced.     

Potential energy surfaces and vibrational spectra for isotopomers of N2O

Potential energy surfaces and vibrational spectra for the four isotopomers (^l5N¹⁴N¹⁶O,^l4N^I5N¹⁶O,¹⁵N₂ ¹⁶O and¹⁵N₂ ¹⁸O) of N₂O have been investigated with the vibrational self-consistent field-configuration interaction method. It is shown that the isotopomers with the same end atom have similar values of the potential parameters, and that substitution with different end atoms can affect the potential obviously. The calculated vibrational levels are in good agreement with the observed values by the optimization of several potential parameters (f ₁ ⁽¹⁾,f ₁₃ ⁽⁰⁾,f ₃ ⁽¹⁾ which are sensitive to isotopic substitutions. Project supported by the National Natural Science Foundation of China (Grant No. 29673029).     

UV Spectrum of the Simplest Deuterated Criegee Intermediate CD2OO

The ultraviolet (UV ) absorption spectrum of the simplest deuterated Criegee intermediate CD₂OO has been measured and compared with that of CH₂OO . While the UV spectra of CH₂OO and CD₂OO are similar in the overall shape, distinctive oscillatory structures at the long wavelength side of the absorption band show clear effect of isotopic substitution. The average spacing between the vibrational peaks decreases from 606 cm⁻¹ for CH₂OO to 528 cm⁻¹ for CD₂OO . This large isotope effect cannot be explained by one‐dimensional model along the dissociative O−O bond. Instead, vibrational modes involving motions of the H‐atoms are expected to be responsible for the observed oscillatory structure. This isotope effect offers a stringent test for theoretical investigations on the absorption spectrum and excited‐state dynamics of the simplest Criegee intermediate.     

Vibrational structure in the photoelectron spectrum of O2+2Σg− (σg2s)

Discrete vibrational structure has been observed in the photoelectron spectrum of oxygen at an ionization potential of 40.33 eV. Two levels, attributed to the O₂⁺²Σ_g^?(σ_g2s) final state, have been detected with a vibrational spacing of 0.071 eV.     

The vibrational spectrum of thionynyl fluoride and its oxygen-18 isotopomer[1]

The vibrational spectrum of thionyl fluoride, SOF₂, has been reinvestigated by means of high resolution infrared and Raman spectroscopy. Substitution of oxygen-16 by oxygen-18 led to a definitive identification of those modes to which sulfur-oxygen motion makes a large contribution. The band structure of the sulfur-oxygen stretching vibration, which is obscured by Fermi resonance with a combination band in S¹⁶OF₂, has been resolved in S¹⁸OF₂. The experimental isotopic splittings are compared with those calculated by previous investigators.     

Ab-initio calculations of Raman, IR-active vibrational modes in isotopically modified B12 icosahedral clusters

Computational calculations of Becke's three-parameter hybrid method using the LYP correlation functional (B3LYP) have been performed on (B₁₂H₁₂)²⁻ dodecaborane anions with different boron isotopic compositions. This was done in order to investigate isotopic dependence of vibrational spectral properties of B₁₂ icosahedra, and for comparison of the optical vibrational properties of the icosahedral molecule with the characteristics of inter- or intra-icosahedral optical phonon vibrational modes in boron-rich crystals.     

The microwave spectrum and large-amplitude vibrations of N-methylaniline

Microwave spectra of the normal and amine-deuterated isotopic species of N-methyl-aniline in the ground and some low-lying excited vibrational states have been observed. The inertial defect indicates that the dihedral angle of the N-CH₃, bond with respect to the ring plane is somewhat less than that for the N—H bonds in aniline. The position of the amino-hydrogen atom is very poorly determined by the isotopic substitution method because of large zero-point effects. The excited vibrational states are consistent with a double-minimum potential for the inversion of the HNCH₃ group and there is some evidence for a lower barrier than in aniline. The excited states of the HNCH₃ torsion indicate a barrier in the range 8 < V₂ < 25 kJ mol^?1 to the internal rotation of this group. No splitting of the ground-state lines attributable to the torsion of the methyl group has been observed, which implies a barrier of V₃ > 8 kJ mol^?1.     

The vibrational relaxation of I2 by H2 in a supersonic jet

The vibrational relaxation of I₂ by H₂ has been studied in a supersonic free jet. It was observed that the addition of 5% H₂ to the helium carrier gas greatly reduces the concentration of X ¹Σ⁺_g(ν″ = 1) I₂ in the jet as compared to the concentration in a pure helium carrier. From this observation we have determined that the average vibrational relaxation cross sections of H₂ is 7.1 times as large as that of helium. Since the average vibrational relaxation cross section of deuterium is at least as large as that of hydrogen, the mechanism responsible for this phenomenon appears not to be dominated by mass effects.     

Determination of vibrational parameters of methanol from matrix-isolation infrared spectroscopy and ab initio calculations. Part 1 – Spectral analysis in the domain 11 000–200 cm

Infrared spectra of three isotopic species of methanol (¹²CH₃¹⁶OH, ¹³CH₃¹⁶OH, ¹²CH₃¹⁸OH) trapped in neon and nitrogen matrices have been recorded between 11 000 and 200 cm⁻¹. Their analysis is based on the isotopic effects which slightly modify the frequencies without significantly changing the nature of vibrations nor the band intensities. From the assignment of most of the two quanta transitions 45 out of the 78 anharmonicity coefficients have been deduced. The value of some of them has been confirmed by the identification of three quanta transitions mainly involving the OH stretching mode. The problem of vibrational resonances between methyl bending and stretching modes has been tackled by performing complementary experiments: use of other isotopic species (CH₃OD, CH₂DOH) and acquisition of Raman spectra in the gas phase.     

Crystal field effects on the ground and lowest excited triplet states of benzene isotopes in a borazine host crystal

The phosphorescence spectra of the C₆H₆C₆H₅D₁p-C₆H₄D₂symp-C₆H₃D₃, C₆D₆ and ¹³CC₅D in a borazine host crystal are analyzed at high resolution. The spectral lines are sharp (～2 cm^?1 wide) indicating that the impurity molecules occupy a unique site in the borazine lattice which is probably substitutional. The phonon sidebands are weak,giving clean, well-resolved spectra much like those of isotopic mixed crystals. In contrast, however, the crystal field effects on the ground state vibrational levels are much smaller than those found for isotopic mixed crystals. The gas-to-crystal shifts are very small, the vibrational degeneracies are not removed and orientational splittings are only observable for a few select vibrational levels. For most vibrational levels and for the derivation of selection rules one can asume the effective crystal site symmetry to be D_3d. The data provide the first conclusive evidence that the splitting observed in the benzene phosphorescence spectrum results from a distortion of the molecule when excited to the zeroth vibrational level of the T₁ state. Furthermore, the data suggest that the distortion is intrinsic in nature (i.e.,is not caused by the crystal field).     

The quantum dynamics of the reactions N+H2(HD,D2) and their vibrational excitation effect

The N(⁴S)+H₂ reaction and its isotopic variants have been investigated by means of time‐dependent quantum wave packet with split operator method on the ground state potential energy surface (Zhai and Han, J. Chem. Phys. 2011, 135, 104314). The reaction probabilities, integral cross sections, branching ratio of the integral cross sections, and effect of vibrational excitation of H₂, HD, and D₂ diatomic molecules are presented and discussed. The results reveal that the intramolecular isotopic effect is greater than the intermolecular one, and that the vibrational excitation of the diatomic molecules can promote the progress of this reaction. In addition, a limited number of rigorous Coriolis coupling calculations of the integral cross sections of the N(⁴S)+H₂ reaction have been carried out. Also shown is that since the Coriolis coupling plays a small part in this accurate quantum calculation, the cheaper centrifugal sudden calculations here reported are effective for this reactive system. © 2014 Wiley Periodicals, Inc.     

The effect of autoionization on the O2 + X2Π g vibrational branching ratios in the wavelength range 905–1,000 Å

Vibrational branching ratios have been measured for the²Π _g ground state of the molecular oxygen ion using photoelectron spectroscopy and monochromated synchrotron radiation. In the wavelength range encompassed by the present study the photoionization cross section is dominated by intense autoionizing resonances, some of which converge onto the O ₂ ⁺ a ⁴Π _u threshold. The resonances cause considerable variations to be observed in the vibrational branching ratios, and the present data have been recorded with sufficient wavelength resolution to determine the profile of these ratios as the wavelength is tuned across an autoionizing resonance.     

A 340 nm emission system in I2 induced by a two-photon excitation process

Iodine vapour is optically excited in a two-step process populating selectively the first four vibrational levels of an ion-pair state having T_e = 47032 ± 6 cm^?1 and ω_e = 98 ± 2 cm^?1. Fluorescence from this state is observed at 340 nm with vibrational resolution and is found to terminate on levels of the intermediate B state.