Abstract
Laser excitation of isotopically labeled SO 2 molecules in a neon matrix has allowed the measurement of dispersed phosphorescence spectra (ã 3 B 1 -X̃ 1 A 1 ) in the wavelength region 387.5-526.3 nm (19 000-25 800 cm -1 ). The origin of the ã-X̃ transition lies at 25 747 cm -1 in 16 OS 16 O, shifted 18 cm -1 to the red from the gas phase; the three vibrational frequencies of the X 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 matrixisolated 16 OS 16 O and 18 OS 18 O 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 ãB 1 (110) at 27 005 cm -1 (370 nm). Two additional groups of bands are observed for the unsymmetrical isotopomer 18 OS 16 O; they are identified as transitions to levels of the ã 3 B 1 state with v 3 = 1 and as direct transitions to the b̃ 3 A 2 state, which both become allowed in the lower symmetry. The v 3 frequency of the ã 3 B 1 state of 18 OS 16 O is 922 cm -1 ; for the b̃ 3 A 2 state, v 1 - 791 cm -1 and v 2 ≃ 315 cm -1 , while the b̃ (001) level z lies 26 653 cm -1 above the X̃ (000) level. © 2000 American Chemical Society.