Cavity ring-down spectroscopy measurements of the concentrations of C 2(X 1Σ g+) radicals in a DC arc jet reactor used for chemical vapour deposition of diamond films

Abstract

Absorption spectroscopy measurements are reported of the absolute number density (3.0 ± 0.9 × 10 12 cm −3) and vibrational temperature (3000 ± 500 K) of C 2(X 1Σ g +) radicals in a DC arc activated chemical vapour deposition reactor under the standard operating conditions (3.3% CH 4 in H 2 and 6.4 kW discharge) used to grow polycrystalline diamond films. The ratio of number densities of C 2 radicals in their ground (X 1Σ g +) and low-lying electronically excited (a 3Π u) states is close to that expected from a Boltzmann distribution at the measured temperature, despite the more rapid rates of reaction of C 2(X) with H 2 and hydrocarbon molecules.