The infrared spectrum of five isotopic forms of the SiH radical by laser magnetic resonance

By employing two different CO-L.M.R.-spectrometers we have observed 52 vibration rotation transitions in five vibrational bands of five isotopic forms of the SiH free radical. A set of ground state vibrational rotational constants has been determined including a precise value of the spin orbit constant A 0 = 142·8957(8) cm-1 from the detection of spin forbidden transitions. The comparison of relative signal amplitudes yields a vibrational temperature near 1600 K for SiH in a discharge of helium, hydrogen and silane in which the walls are at room temperature.