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A new set of wavenumbers for the Stimulated Raman Spectrum (SRS) of the ν1 band of 12CH4 is presented using the Infrared (IR) absorption spectrum of the P10 component of ν3 of the same molecule as a wavenumbers standard. An estimation of the Stark shift due to the pump laser field is experimentally deduced what allows to extrapolate the measured wavenumbers to zero field amplitude. A careful discussion about the main possible error sources and how to cope with them is also included.The absolute accuracy of the wavenumbers set presented here is believed to be at least one order of magnitude better as compared with previous measurement.

Collisional broadening, line shifting, and line mixing in the stimulated Raman 2ν2 Q branch of CH4 J. Chem. Phys. 95, 7938 (1991); 10.1063/1.461322 Rotationally inelastic rates for N2-N2 system from a scaling theoretical analysis of the stimulated Raman Q branch J. Chem. Phys. 89, 5568 (1988); 10.1063/1.455563Rotational collisional narrowing in the NO fundamental Q branch, studied with cw stimulated Raman spectroscopyThe fundamental isotropic Raman Q branch of oxygen at pressures up to 2 atm and for temperatures between 295 and 1350 K has been recorded using stimulated Raman gain spectroscopy (SRGS) for collisions with oxygen and nitrogen. The line broadening and line shifting coefficients have been determined for several rotational quantum numbers (up to N = 55 at 1350 K). The temperature dependence of these coefficients has also been studied for most of the rotational lines. The line parameters (widths and shifts) have been then calculated a priori through a semiclassical model. A good agreement between experimental and theoretical data has been observed. Another theoretical approach based on fitting and scaling law has been used to calculate the line broadening coefficients. It is shown that a modified exponential energy gap model (MEG) and an energy corrected sudden law (ECS) for the state-to-state rotationally inelastic rates, account for the rotational and temperature dependences of the observed line widths. With regard to the energy corrected sudden law, the best results are obtained when the basis rate constants are modeled with a hybrid exponentialpower fitting law (EP). The line broadening and shifting coefficients of the oxygen-nitrogen mixture are very close to those found for pure oxygen.

The transition dipole moment of the v3 band of the methyl radical has been measured for the first time. A new discharge laser amplitude double modulation method with a difference frequency laser spectrometer and a hollow cathode discharge cell has been used. The CH3 concentration has been estimated from the absorption decay when the discharge is turned off. The transition dipole moment is found to be pv, = 0.029 f 0.005 D.

Self-broadened nitrogen isotropic Q(J) Raman linewidths have been inverted to obtain effective rotation–translation (R–T) state-to-state rate constants using the energy corrected sudden (ECS) formalism. These rate constants are discussed as a function of the rotational levels J and temperature T. Collisional Q(J) line shifts have been investigated by high-resolution inverse Raman spectroscopy (IRS) over a wide temperature range. Semiclassical calculations lead to a clear understanding of their J and T dependence. This exhaustive study of both diagonal and off-diagonal relaxation matrix elements has allowed us to calculate the collisionally narrowed Q branch at high pressure. New measurements of N2 Q branch at high pressure have been performed by IRS. The good agreement of ECS profiles with IRS data, for various pressures and temperatures, underlines the consistency of the present R–T ECS scaling analysis.

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The characteristics of a commonly used pulsed valve for the production of free jets and molecular beams are analyzed in detail. Special attention is paid to the formation of gas pulses providing a quasisteady flow during a certain time interval within the pulse duration, and to the estimation of a scaling parameter (effective diameter) for the description of the flow field. The adequacy of this effective diameter is checked by performing time-of-flight measurements on molecular beams of Ne, N2, and CH4, and stimulated Raman spectra on free jets of N2 and CH4. 0 1995Americun Tnstitute of Physics.

We report a stimulated Raman spectrum of the Q branch of the V3 band of ethane recorded with a resolution of about 0.0055 cm -I and an absolute wave-number accuracy of the order of 0.001 cm -I. This spectrum is analyzed in terms of a vibrational-torsional coupling Hamiltonian that allows for the calculation of the observed wave numbers within the experimental u~certainty. The following spectroscopic parameters (in cm -I) have been obtained: v3=994.1108( 10), B'j's-Bo= -0.006165(3), B'fd_BO= -0.006170(2), B'fs-B o = -0.006184(2), JJ13d_B o = -0.006 257(2), A1Is-Ao= -0.003 037( 15), A'fd_Ao = -0.003 040(12), A'fs-A o = -0.003054(12), and A1 3d _A o = -0.003 065(12). A strong dependence of the threefold torsional potential barrier with respect to the q3 normal mode, aV 3 1aQ3= -275.9± 1.4 cm-I , is deduced from the present analysis.