The spectrum of sulfur dioxide in inert matrices at 4°K

Abstract

A reliable and reproducible procedure has been developed for obtaining the low temperature matrix isolation absorption spectra of molecules in the ultraviolet and vacuum ultraviolet region. A ratio of about 100 matrix atoms to 1 molecule gives the sharpest spectrum, and a deposition rate of about 16 cc/hr. of air at S.T.P. gives the most transparent matrix. The absorption spectra of sulfur dioxide vapor and of matrix isolated sulfur dioxide are obtained between 2250 and 1900 A with a 0.5 meter vacuum ultraviolet monochromator. Wavelength measurements of 19 strong bands in an argon matrix, and in a neon matrix are made and compared with vapor phase measurements. An analysis of the shift in the absorption spectrum of the trapped sulfur dioxide indicates that all of the observed bands belong to a single electronic transition. A shift of the observed bands in an argon matrix, 34 cm⁻¹ to the blue, and in a neon matrix, 106 cm⁻¹ to the red, relative to the bands in the vapor shows that for the 2000 A system of sulfur dioxide the dipole moment in the excited state is less than the dipole moment in the ground state. The shift of vibrational frequencies in the excited state compares favorably with the predictions given by Buckingham's theory for shifts of the vibrational frequencies of trapped molecules in their ground state. Some comments are made regarding the vibrational analysis of the system.