The Doppler-free spectrum and the Zeeman effect of the A 1B1u(v4=1:b1u)←X 1Ag(v=0) transition of naphthalene in the 33 576.4–33 578.0 cm−1 range has been measured by means of two-photon absorption spectroscopy with counter propagating light beams of identical wavelength within an external cavity. Rotational lines were fully resolved, and 1098 Q(K)Q(J) lines of J=0–42, K=0–24 were assigned. The molecular constants of the A 1B1u(v4=1:b1u) state were determined. Deviations from the line positions calculated using the molecular constants were observed for several lines. Perturbations were not observed for K=0 but were observed to increase with increasing K. The perturbations were therefore identified as originating from a parallel Coriolis interaction. The Zeeman splittings for lines of a given J were observed to be maximum at K=0 and to decrease with increasing K. Analysis of these results indicate that the magnetic moment lies along the c axis (perpendicular to the molecular plane). Any lines broader than our instrumental resolution (5 MHz) were not observed at H=0 T. The J and K dependence of the Zeeman splittings of the A 1B1u(v4=1:b1u)←X 1Ag(v=0) transitions were observed to be regular. This observation and the small number of perturbed lines, leads to the conclusion that the resonance interaction of the A 1B1u state with the T1 3B3u and T2 3B1u states are small and negligible in the observed region.

Doppler-free two-photon excitation spectrum and the Zeeman effect of the S1 1B1u(v21=1) <-- S0 1Ag(v=0) transition of naphthalene-d8 have been measured. 908 lines of Q(Ka)Q(J)KaKc transition of J=0-41, Ka=0-20 were assigned, and the molecular constants of the S1 1B1u(v21=1) state were determined. Perturbations were observed, and those were identified as originating from Coriolis interaction. No perturbation originating from an interaction with triplet state was observed. The Zeeman splittings from lines of a given J were observed to increase with Kc, and those of the Kc=J levels increased linearly with J. The Zeeman effects are shown to be originating from the magnetic moment of the S1 1B1u state, which is along the c axis and is induced by mixing of the S2 1B3u state to the S1 1B1u 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 S1 1B1u state does not occur through the intersystem mixing. This is at variance with generally accepted understanding of the pathways of the nonradiative decay.

No abstract

A Doppler-free absorption spectrum and the Zeeman effect of the A 1B2u(v14=1,v1=1)←X 1A1g(v=0) transition of benzene have been measured by means of two-photon absorption spectroscopy with counterpropagating light beams of identical wavelength within an external cavity. Rotational lines were fully resolved, and 647 QQ lines of J=0–43, K=0–43 have been assigned. The molecular constants of the A 1B2u(v14=1,v1=1) state have been determined as A=B=0.181 046 1, C=0.090 548 9, DJ=0.544×10−7, DJK=−1.093×10−7, DK=0.587×10−7, and T0=40 578.2672 cm−1. The Zeeman splittings for lines of a given J were observed to increase regularly with K and reach a maximum at K=J. This demonstrates that the magnetic moment lies along the c axis (perpendicular to the molecular plane). The magnetic moment of the A 1B2u(v14=1,v1=1,J=43,K=43) level was determined to be 0.005μB. The Zeeman splittings of the K=J levels were observed to increase with increasing J. Via analysis of the rotationally resolved Zeeman spectra, it is concluded that the A 1B2u state is mixed with the E2u3 state. This new finding suggests that vibronic interactions between E2u3 and B1u3(T1) and between E2u3 and E1u3(T2) through the mixed E2u3 component, contribute to the B2u1(S1)→3B1u(T1) and B2u1(S1)→3E1u(T2) intersystem crossings, respectively.

Doppler-free two-photon fluorescence excitation spectra of the Ã 1Au(v7′=1)←X̃ 1Ag(v″=0) transition of trans-glyoxal were measured by propagating a laser beam either polarized parallel (π pump) or perpendicular (σ pump) to the magnetic field of 6 T. π pump and σ pump dependence of the Zeeman spectra of the Q(J=6)Q(K) lines for K=0–6 was measured. Intensities of the Zeeman components of the Q(6)Q(6) lines were observed to have the maxima at the high and low wave number ends and the minimum at the middle for π pump, and the minima at the high and low wave number ends and the maximum at the middle for σ pump. By comparing calculated and observed patterns of the Zeeman spectra, it became clear that the transition tensor M00 is dominant and the effective intermediate state is 1 1Bu(ππ*). K dependence of the Zeeman spectra of the Q(J=15)Q(K) lines was measured, and the Zeeman splittings were observed to increase proportionally to K2. J dependence of the Zeeman spectra of the Q(J)Q(K=J) lines was measured for J=0–15, and the Zeeman splittings was found to increase proportionally to J. The K and J dependence of the Zeeman splittings were analyzed. It is concluded that the Zeeman splitting of the Ã 1Au(nπ*) state is originating from the mixing of the 1 3Bu(ππ*) state by spin–orbit interaction, and the magnetic moment is along the molecular top axis.