High resolution Raman spectroscopy from vibrationally excited states populated by a stimulated Raman process:: 2ν2-ν2 of 12C2H2 and 13C2H2

A generalization of a previously reported technique for investigating vibrationally excited states via high resolution Raman spectroscopy is proposed. In a first step, a vibrational state, typically not accessible by a dipole moment transition from the ground state, is populated in a pulsed stimulated Raman process. After a delay of several nanoseconds, a high resolution spectrum corresponding to transitions from this long Lived state is recorded following a quasi-cw stimulated Raman spectroscopy scheme. The use of a pulsed dye laser for providing one of the pumping radiations overcomes some of the limitations of the previously proposed scheme, where this radiation was generated by a Raman shifter filled at relatively high pressure with the gas under study. Experimental aspects are discussed and the spectra of the Q branches of 2 nu(2)(Sigma(g)(+))-nu(2)(Sigma(g)(+)) of (C2H2)-C-12 and (C2H2)-C-13 are presented. The analysis of the measured transitions yielded accurate values of the spectroscopic parameters for the upsilon(2)=2 vibrationally excited state for both isotopomers and improved values of the corresponding anharmonicity constants x(22)(0) are derived. (C) 1998 American Institute of Physics.