We present a detailed spectral study of the atmospherically important methylthio (CH3S) radical demonstrating the advantage of IR-VUV photoionization for vibrational spectroscopy of free radicals due to its mass selectivity. Photolysis of CH3SH produced CH3S radicals that were ionized with (1 + 1) IR-VUV photoionization and detected with the time-of-flight technique. The IR spectrum of CH3S was obtained in the range 2790-3270 cm (1). Absorptions features near 2819 and 2904 cm (1) are assigned to nu(1) and nu(4) modes of CH3S, respectively, and those near 2978 and 3241 cm (1) are tentatively assigned as combination transitions 3(1)5(1)6(1)(e) and 3(1)5(1)6(1)(a), respectively, from the ground vibrational state. (C) 2011 Elsevier B.V. All rights reserved.