REMPI SPECTROSCOPY OF SO SINGLET-STATES

Three newly found vibrational levels at energies T-e(upsilon) = 45127. 88(3), 51900.40(4), and 52604.95(3) cm(-1) allow the first application of resonance-enhanced multiphoton ionization for detecting the SO rad ical in its low-energy singlet states, a(1)Delta and b(1)Sigma(+). The analysis of the spectra is based on the observation of 10 rotationall y resolved bands starting from a(1)Delta upsilon = 0, 6... 11 and b(1) Sigma(+) upsilon = 8, covering a typical range of J = 5...40 or 50. Po pulation of these SO singlet states has been achieved by two-photon di ssociation of SO2 in a molecular beam environment, applying wavelength s in the 248 to 291 nm range. This paper presents an analysis of the r otational, vibrational, and electronic properties of the new levels. R eviewing earlier works on the singlet states of SO, a revised term ene rgy scheme is provided which connects the singlet and triplet systems of the molecule. (C) 1998 Academic Press.