Spectroscopy and intramolecular relaxation of methyl salicylate in its first excited singlet state

High resolution fluorescence excitation experiments are reported for the blue emitting rotamer of methyl salicylate in its first excited singlet state. These experiments employ moderate expansions of methyl salicylate seeded in argon ( P0D=5–8 Torr cm) to achieve rotational and vibrational cooling in a pulsed supersonic jet. The rotational contour of the electronic origin at 30 055.3 cm−1 is shown to be consistent with a geometrically distorted π−π* excited state, partially polarized along the A axis and with a rotational temperature of 5–7 K. A noticeable broadening of the spectral features beyond the rotational contour begins at 500 cm−1 above the origin and then increases rapidly above 900 cm−1 reaching a width of 12 cm−1 near 1200 cm−1. The constancy of fluorescence decay lifetimes in this region indicate that intramolecular vibrational relaxation in the S1 manifold is the broadening mechanism.