The CN and CS transient species in CH3SCN discharges

Abstract

The plasma chemistry of transient species in methyl thiocyanate (CH 3SCN) dc discharges was studied semi-quantitatively using spectroscopic techniques. The vibrational spectra of CS and CN diatomic species in these plasmas have been recorded using mid-infrared diode laser absorption spectroscopy (TDLAS). Concentrations of about 1012 and 10 13-1014 cm-3 were determined for CN and CS, respectively. It was also found that under high plasma current conditions, the concentration of ground state CN showed a decrease, while that of CS exhibited opposite behavior. The generation and loss of CN and CS were explained through a combination of key electron impact processes and radical-molecule reactions. One of the most abundant discharge products with a concentration of about 1015 cm-3 is isothiocyanic acid (HNCS) also detected using TDLAS. Surface as well as gas phase reactions contributed to its abundance in the plasma. Other species such as HCN and CS2 were detected with Fourier transform infrared spectroscopy, while the electronic emission spectra of CN, CS, CH, N2* and NH were also recorded using optical emission spectroscopy. © 2004 Elsevier B.V. All rights reserved.