A new absorption spectrum in the region 4600–5600 Å has been discovered in the flash photolysis of silyl iodide, SiH3I. A rotational analysis, together with the observation of a deuterium isotope shift, has shown that the spectrum is due to the HSiI radical.The lower electronic state of HSiI is a 1A′ state with a bond angle of ~103°, and the upper state is 1A″ with angle ~116°. Axis-switching effects, due to the increase in bond angle, cause the appearance of ΔK = 0, ± 2 subbands, in addition to the ordinary ΔK = ± 1 subbands.