Doppler-Free Two-Photon Excitation Spectroscopy and the Zeeman Effect in the “Channel Three” Region of C6H6

Abstract

Abstract Doppler-free two-photon excitation spectra and the Zeeman effects for the 1021401 and 1011401 bands, whose vibrational excess energies are 3412 and 2492 cm−1, respectively, of the S11B2u ← S01A1g transition in gaseous benzene-h6 have been measured. Rotationally resolved lines up to a rotational excess energy of 945 cm−1 in the 1011401 band, whose excess energy is isoenergetic with the one of the 1021401 band at low J, have been observed. The density of perturbation is observed to increase around the K = 0 and K = J levels in the 1011401 band as the rotational energy increases, but line broadening is not observed. It was reported that only the K = 0 lines at low J and the K = J lines at high J were observed as a sharp line and the rest was washed out by broadening in the 1021401 band. The assignments are confirmed by the Zeeman spectra. The character and magnitude of Zeeman splittings in both bands could be understood as originating from the electronic orbital angular momentum arising from a mixing of the S11B2u and S21B1u states via J–L coupling. The levels of the S11B2u state are found not to be mixed with a triplet state by the Zeeman effect.