HIGH-RESOLUTION IONIZATION-DETECTED RAMAN GAIN SPECTROSCOPY OF N-2 AND C6H6

Double resonance spectra have been obtained for nitrogen and benzene m olecules in the low density region of a molecular beam by use of stimu lated Raman pumping followed by ionization probing. For N-2 the photoi onization step was via a 2+2 resonantly enhanced multiphoton ionizatio n process using the a(1) Pi(g)(v = 2)<--X(1) Sigma(g)(v = 1) two-photo n resonance. The detection limit is 10(3)-10(4) times lower than for t he direct optical measurement of a stimulated Raman signal. For benzen e, a more efficient 1+1 ionization step permitted measurements at stat e densities less than 10(10) cm(-3) and the Raman step yielded linewid ths of 30 MHz for the Q-branch lines of the weak Raman active nu(16) f undamental. (C) 1996 American Institute of Physics.