OBSERVATION OF THE SCL RADICAL BY RESONANCE-ENHANCED MULTIPHOTON IONIZATION SPECTROSCOPY

We report the first observation of any excited electronic state of the SCI radical. SCI (X (II)-I-2) radicals are produced by photolysis of SCl2 vapour at near-UV wavelengths around 343 nm, and detected by multiphoton ionisation spectroscopy, resonance enhanced at the two-photon energy by a Rydberg state of (II)-I-2 electronic symmetry. We suggest that this state derives from an electronic configuration involving a 4p pi Rydberg electron built on the (3) Sigma-ground-state ion core. Analysis of the (partially) rotationally resolved resonance-enhanced multiphoton ionisation (REMPI) spectra seems most fully consistent with all transitions originating exclusively from X (II3/2)-I-2 levels of both the (SCl)-S-32-Cl-35 and (SCl)-S-32-Cl-37 isotopomers and yields the term value for the newly identified (II)-I-2 state (v(0) = 58 220 +/- 20 cm(-1)) measured relative to the lower (X (II3/2)-I-2) Spin-orbit component of the ground state. The excited state is shown to have a bond length ca. 13% shorter than that of the ground-state neutral. Parallel REMPI-photoelectron spectroscopy (PES) studies yield values of 9.57 +/- 0.01 eV for the first ionisation energy (E(i)) of SCI (measured relative to the lower, (II3/2)-I-2, spin-orbit component of the ground state), and 685 +/- 30 cm(-1) for the vibrational level separation in the ground-state ion (ca. 19% higher than that of the corresponding energy interval in the ground-state neutral).