The laser magnetic resonance spectrum of HCl+t

Pure rotational spectra have been obtained for only a very limited number of molecular ions [1]. Both microwave spectroscopy and millimetre wave astronomy have been employed for the study of CO + [2], HCO + [3], HNN + [4] and HCS + [5]. In a previous paper [6] the first detection of rotational transitions of a molecular ion (HBr +) by far-infrared laser magnetic resonance spectroscopy of a longitudinal d.c. discharge was reported. In this article we describe the first detection of the pure rotational spectrum of HC1 ÷ with a laser magnetic resonance spectrometer employing a transverse intracavity positive column discharge. The HCI+ molecular ion has received considerable attention in recent years. Its electronic spectra have been the subjects of several theoretical treatments aimed at establishing the relationship between the electron spin-nuclear rotation interaction and centrifugal distortion of the spin-orbit interaction and their respective isotopic and vibrational dependences [7, 8]. While a chlorine-containing molecule has not yet been observed in an interstellar dust cloud [9]