VIBRATIONAL STRUCTURE IN THE LOW-ENERGY REGION OF THE 1A2 STATE OF SO2

Molecular beam fluorescence excitation spectra of sulphur dioxide in the wavelength range 348-334 nm are presented. Identification of cold transitions is accomplished by controlled variation of vibrational temperature, and narrow rotational contours permit accurate determination of the corresponding vibrational band origins. These data conform well with the proposed assignment of 1A2-1A1 vibrational progressions of Hamada and Merer, although different progressions are found to display markedly different intervals. The energy below which bands of the 3B1-1A1 transition exceed those of the 1A2-1A1 system in intensity is found near 347 nm.