High resolution ionization-detected Raman gain spectroscopy of N2 and C6H6

Abstract

Double resonance spectra have been obtained for nitrogen and benzene molecules in the low density region of a molecular beam by use of stimulated Raman pumping followed by ionization probing. For N2 the photoionization step was via a 2+2 resonantly enhanced multiphoton ionization process using the a1Πg(v=2)←X1Σg(v=1) two-photon resonance. The detection limit is 103–104 times lower than for the direct optical measurement of a stimulated Raman signal. For benzene, a more efficient 1+1 ionization step permitted measurements at state densities less than 1010 cm−3 and the Raman step yielded linewidths of 30 MHz for the Q-branch lines of the weak Raman active ν16 fundamental.