Laser-induced phosphorescence of SO2 in solid neon: Direct observation of the (b)over-tilde(3)A(2) state in the (OSO)-O-16-O-18 molecule

Laser excitation of isotopically labeled SO2 molecules in a neon matrix has allowed the measurement of dispersed phosphorescence spectra ((a) over tilde(3)B(1)-(X) over tilde(1)A(1)) in the wavelength region 387.5-526.3 nm (19 000-25 800 cm(-1)). The origin of the (a) over tilde-(X) over tilde transition lies at 25 747 cm(-1) in (OSO)-O-16-O-16, shifted 18 cm(-1) to the red from the gas phase; the three vibrational frequencies of the (X) over tilde state are nearly unperturbed in the neon matrix (1149, 520, and 1362 cm(-1)). As the zero-phonon lines are sharp and well resolved, it has been possible to monitor emission from a specific isotopomer to obtain its excitation spectrum. The excitation spectra of matrix-isolated (OSO)-O-16-O-16 and (OSO)-O-18-O-18 in the region 350.9-388.5 nm (25 740-28 500 cm(-1)) are similar to those previously observed in the gas phase, with strong perturbations affecting all vibrational levels above a(3)B(1)(110) at 27 005 cm(-1) (370 nm). Two additional groups of bands are observed for the unsymmetrical isotopomer (OSO)-O-18-O-16; they are identified as transitions to levels of the (a) over tilde(3)B(1) state with v(3) = 1 and as direct transitions to the (b) over tilde(3)A(2) state, which both become allowed in the lower symmetry. The v(3) frequency of the (a) over tilde(3)B(1) state of (OSO)-O-18-O-16 is 922 cm(-1); for the (b) over tilde(3)A(2) state, v(1) similar or equal to 791 cm(-1) and v(2) similar or equal to 315 cm(-1), while the (b) over tilde (001) level lies 26 653 cm(-1) above the (X) over tilde (000) level.