Sub-Doppler rotationally resolved spectroscopy of the [formula omitted] bands of benzene and benzene- d6

Abstract

Sub-Doppler excitation spectra of the S 1 1B 2u(v 6=1)←S 0 1A 1g(v=0) transition of the C 6D 6 and C 6H 6 molecules were measured by crossing a laser beam perpendicular to a collimated molecular beam. Part of a scanning laser beam was passed through the actively stabilized etalon, whose cavity length was locked against the wavelength of the cw Nd:YAG laser which was locked to a hyperfine line of an iodine molecule, and the fringe marks at every 60 MHz were used to measure the change of the laser frequency precisely. Rotationally resolved 1253 and 1158 lines of C 6D 6 and C 6H 6, respectively, were used to determine molecular constants of the S 1 1B 2u(v 6=1) and S 0 1A 1g(v=0) states. No appreciable perturbations were observed in the S 0 1A 1g(v=0) and S 1 1B 2u(v 6=1) states of both molecules. From the improved molecular constants, the internuclear distances r C–C and r C–H were determined to be 1.39711 and 1.08066 Å, respectively, in the S 0 1A 1g(v=0) state, and 1.4317 and 1.072 Å, respectively, in the S 1 1B 2u(v 6=1) state.