A resonance Raman study of ethylene has been performed with the use of excitation wavelengths ranging from 200 to 141 nm. Excitation resonant with the V(ππ*) state results in Raman spectra exhibiting intensity in the C=C stretching vibration, the CH2 symmetric scissors vibration, the CH2 torsional vibration and the CH2 out‐of‐plane wagging vibrations. These spectra confirm that the V state is strongly twisted about the C–C bond. They also indicate that the C=CH2 groups are no longer planar in the V state. Resonance with the (π3s) and (π3p) Rydberg transitions results in spectra exhibiting much less intensity in the torsional vibration, the CH2 symmetric scissors vibration and the CH2 wagging vibrations. The spectrum obtained in resonance with the (π3d) Rydberg transitions once again exhibits activity in the CH2 symmetric scissors mode.

Vacuum ultraviolet resonance Raman studies of the excited electronic states of ethylene

Vibrational levels and anharmonicity in SF6—I. Vibrational band analysis

A comprehensive study of a steady axisymmetric supersonic jet of CO2, including experiment, theory, and numerical calculation, is presented The experimental part, based on high-sensitivity Raman spectroscopy mapping, provides absolute density and rotational temperature maps covering the significant regions of the jet: the zone of silence, barrel shock, Mach disk, and subsonic region beyond the Mach disk The interpretation is based on the quasi-gasdynamic (QGD) system of equations, and its generalization (QGDR) considering the translational–rotational breakdown of thermal equilibrium QGD and QGDR systems of equations are solved numerically in terms of a finite-difference algorithm with the steady state attained as the limit of a time-evolving process Numerical results show a good global agreement with experiment, and provide information on those quantities not measured in the experiment, like velocity field, Mach numbers, and pressures According to the calculation the subsonic part of the jet, downstream of the Mach disk, encloses a low-velocity recirculation vortex ring

https://digital.csic.es/bitstream/10261/24220/1/JFM2001.PDF

Experimental and numerical investigation of an axisymmetric supersonic jet

In a crossed molecular beam experiment total differential cross sections and differential energy loss spectra have been measured for Ne + CH4 at 88·8 meV. The energy loss spectra taken at centre-of-mass deflection angles from 45° to 145° show appreciable energy transfer in the backward direction with a maximal energy transfer corresponding to final rotational states of j′ = 4. The total differential cross sections exhibit diffraction oscillations in the forward direction. These two data sets are compared with calculations performed in the accurate centrifugal sudden approximation both for the A- and T-symmetry of the CH4 molecule. The non-spherical potential surface, which includes the anisotropic T 3 and T 4 is determined from accurate SCF-calculations and a damped dispersion contribution using the HFD-model. The general features of the experimental data are reproduced using a simple universal damping function. However, discrepancies concerning the isotropic potential well depth and the repulsive anisotr...

Rotationally inelastic scattering and potential calculations for He + CH4

All known vibrational energies in 12C2H4([Xtilde]1 Ag ) are collected. A block-diagonalized vibrational matrix Hamiltonian is set up, combining a Dunham expansion with the 2/10,10, 11/2,12, and the 5,5/9,9, 1,1/11,11,1,9/5,11 and 1,11/5,9 anharmonic resonances, with the normal modes numbered according to the most usual conventions in the previous literature. A step by step fitting procedure is applied. Vibrational constants are obtained, and vibrational assignments are provided and discussed. A slightly modified ensemble of vibrational constants is also produced by taking care of a more extended set of resonances between the CH-type vibrations. A new constant of the motion N = 3ν1 + 3ν5 + 3ν9 + 3ν11 + 2ν2 + ν10 + ν12 is demonstrated to support the latter vibrational energy pattern.

G. Luijks

Papers

Molecular beam diagnostics by Raman scattering

Raman analysis of SF6 molecular beams excited by a cw CO2 laser

Molecular beams of CF3Br probed by spontaneous raman effect and excited with a CO2 laser

Raman analysis of C2H4 molecular jets excited by a cw CO2 laser

IR two-photon excitation of ethylene, reconsidered