Detection of CH in an expanding argon/acetylene plasma using cavity ring down absorption spectroscopy

Cavity ring down (CRD) absorption spectroscopy is used to measure the methy lidyne (CH) radical in an Ar/C2H2 plasma. The rotational spectrum of the A( 2)Delta(nu' = 0) <-- (XII)-I-2(nu "= 0) transition around 430 nm is recorde d to determine the total CH ground state density, both as a function of the current through the are producing the low-pressure Ar plasma and as a func tion of the injected acetylene flow. Total ground state densities between 5 X 10(15) and 8 X 10(16) m(-3) are detected. The trends show that the methy lidyne radical plays a minor role in the growing mechanism of hydrogenated amorphous carbon films and is predominantly formed in the charge exchange/d issociative recombination channel starting from the C2H radical. (C) 1999 E lsevier Science B.V. All rights reserved.