Rotationally resolved high-resolution spectrum of the S(1)-S(0) transition of jet-cooled thioanisole.

The rotationally resolved high-resolution fluorescence excitation spectrum of the 0-0 band in the S(1)← S(0) electronic excitation of thioanisole was observed using the techniques of a collimated supersonic jet and a single-mode ultraviolet laser for the first time. High accurate rotational constants for the S(0) and the S(1) states have been determined by precisely calibrated transition energies of about 1000 assigned rotational lines. The molecular structure of thioanisole has been estimated by high-level MO calculations. The planarity of thioanisole in the S(0) and the S(1) states was also demonstrated clearly. The lifetime of the S(1) state was estimated to be 2.0 ns from the observed line width. This line shape did not change with the magnetic field of 1 Tesla, suggesting that the main radiationless process should be internal conversion to the S(0) state.