Doppler-free two-photon excitation spectroscopy and the Zeeman effects of the S1 1B1u(v21=1)←S0 1Ag(v=0) band of naphthalene-d8 -: art. no. 144303

Doppler-free two-photon excitation spectrum and the Zeeman effect of the S-1 B-1(1u)(v(21)=1)<- S-0 (1)A(g)(v=0) transition of naphthalene-d(8) have been measured. 908 lines of (Q(K)(a))Q(J)(Ka)K-c transition of J=0-41, K-a=0-20 were assigned, and the molecular constants of the S-1 B-1(1u)(v(21)=1) state were determined. Perturbations were observed, and those were identified as originating from Coriolis interaction. No perturbation originating from an interaction with a triplet state was observed. The Zeeman splittings for lines of a given J were observed to increase with K-c, and those of the K-c=J levels increased linearly with J. The Zeeman effects are shown to be originating from the magnetic moment of the S-1 B-1(1u) state, which is along the c axis and is induced by mixing of the S-2 B-1(3u) state to the S-1 B-1(1u) state by J-L coupling. Rotationally resolved levels were found not to be mixed with a triplet state from the Zeeman spectra. Accordingly, it is concluded that nonradiative decay of an isolated naphthalene excited to low rovibronic levels in the S-1 B-1(1u) state does not occur through the intersystem mixing. This is at variance with generally accepted understanding of the pathways of the nonradiative decay. (C) 2005 American Institute of Physics.