The electronic absorption spectrum of thiazyl fluoride shows two band systems between 405 and 215 nm. The longer wavelength system, with origin at 25 488 cm–1, exhibits long progressions in ν′1= 984 cm–1 and ν′3= 315 cm–1. There are also many hot bands involving up to three quanta of ν″3, particularly at the red end of the spectrum. The bands in this system have sharp rotational structure, the degradation of which indicates that the valence angle in the excited state is less than in the ground state, as in the analogous band system of the isoelectronic molecule SO2. The shorter wavelength system, with origin at 42 341 cm–1, consists principally of one short progression in ν′1= 1090 cm–1.