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Bruno, A. E.; Riedle, Eberhard ORCID: 0000-0002-2672-5718; Neusser, H. J. (1986): Sub-doppler two-photon spectrum of asymmetric rotor molecules. Analysis of the qqQ rotational branch of the S1(1B2u)141 ← S0(1A1g) system of benzene-d1. In: Chemical Physics Letters, Vol. 126, No. 6: pp. 558-566


The Doppler-free two-photon excitation spectrum of the qqQ branch of the 1410 vibrational band of the S1(1B2u) ← S0(1A1g) transition of benzene-d1 has been recorded using a cw single-mode dye laser coupled to an external concentric resonator. The spectrum has been analysed using a non-rigid Watson Hamiltonian. More than 200 lines with J up to 20 have been assigned and the rotational constants which best reproduce the spectrum are A1v = 0.181435, B1v = 0.169990, C1v = 0.089055 cm−1. The Ka = odd lines of the qqQ5(J) subbranch show small and quite regular perturbations of 60 ± 5 MHz which are probably due to a coupling to another vibrational state of the S1 manifold.