Two-photon vibronic transitions in crystalline chrysene

Abstract

The two-photon (TP) absorption spectrum of crystalline chrysene has been measured at 10 K in the wavelength region 370–300 nm. Vibronic transitions to the first excited level L b (B u) are observed due to b u vibrations of CC stretching character. Evidence of strong crystal field effects on electronic levels is found in our spectrum. The energy splitting between the two crystal origins is estimated to be ≈ 400 cm −1 in good agreement with previous observations. The TP absorption spectrum is accordingly discussed in terms of crystal, rather than molecular, states. Calculation of vibronic coupling coefficients for all b u vibrational modes with frequency < 1700 cm −1 by means of the orbital following method helps identifying the most active b u modes in the vibronic structure of the L b (B u) state. Application of the oriented-gas model on calculated TP tensors shows that b u vibrations induce intensity for both crystal origins, in good agreement with experimental results. Vibronic coupling is also responsible for TP absorption in the first excited A g state, 2A g.