HIGH-RESOLUTION RAMAN-SPECTROSCOPY FROM VIBRATIONALLY EXCITED-STATES POPULATED BY A STIMULATED RAMAN PROCESS - 2-NU(2)-NU(2) OF (C2H2)-C-12AND (C2H2)-C-13

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 accessi ble by a dipole moment transition from the ground state, is populated in a pulsed stimulated Raman process. After a delay of several nanosec onds, a high resolution spectrum corresponding to transitions from thi s long Lived state is recorded following a quasi-cw stimulated Raman s pectroscopy scheme. The use of a pulsed dye laser for providing one of the pumping radiations overcomes some of the limitations of the previ ously proposed scheme, where this radiation was generated by a Raman s hifter filled at relatively high pressure with the gas under study. Ex perimental 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 accur ate values of the spectroscopic parameters for the upsilon(2)=2 vibrat ionally excited state for both isotopomers and improved values of the corresponding anharmonicity constants x(22)(0) are derived. (C) 1998 A merican Institute of Physics.