Pendular-state spectroscopy of the $S1–S$ electronic transition of 9-cyanoanthracene

Fluorescence excitation spectra of the $S1–S0$ origin band of 9-cyanoanthracene have been observed under a uniform electric field up to 200 kV/cm to explore pendular-state spectrum of an asymmetric-top molecule close to the strong field limit. The observed spectra exhibit distinct evolution of the band contour as a function of the applied electric field, which are much different from each other for different excitation configurations. An approximate method suitable for spectrum simulations of large asymmetric-top molecules in a pendular condition is developed for the analysis of the experimental results. The comparison of the observed and simulated spectra shows that the spectra are well ascribed in terms of the pendular-state selection rules, which have recently been derived from theoretical consideration of the pendular-limit representation of energy levels and spectra [R. Kanya and Y. Ohshima, Phys. Rev. A 70, 013403 (2004)].