HIGH-RESOLUTION LASER SPECTROSCOPY OF THE S1 _ S0 TRANSITION OF Cl-NAPHTHALENES

High-resolution fluorescence excitation spectra of the $S_{1} leftarrow S_{0}$ electronic transition have been observed for 1-Cl naphthalene (1-ClN) and 2-Cl naphthalene (2-ClN). Sub-Doppler excitation spectra were measured by crossing a single-mode UV laser beam perpendicular to a collimated molecular beam. The absolute wavenumber was calibrated with accuracy 0.0002 cm$^{-1}$ by measurement of the Doppler-free saturation spectrum of iodine molecule and fringe pattern of the stabilized etalon. For 2-ClN, the rotationally resolved high-resolution spectra were obtained for the $0^0_0$ and $0^0_0+1042$ cm$^{-1}$ bands, and these molecular constants were determined in high accuracy. The obtained molecular constants of the $0^0_0$ band are good agreement with the ones reported by Plusquellic {it et. al.} footnote{D. F. Plusquellic, S. R. Davis, and F. Jahanmir, {em J. Chem. Phys.}, {bf 115}, 225 (2001).} For the $0^0_0+1042$ cm$^{-1}$ band, the local energy shifts were found. On the other hand, for 1-ClN, the rotational lines were not fully resolved because the fluorescence lifetime is shorter than the one of 2-ClN. Then we determined the molecular constants of 1-ClN from the comparison the observed spectrum with calculated one