Rotational temperature measurements of excited and ground states of C2(d3Πg-a3Πu) transition in a H2/CH4 915 MHz microwave pulsed plasma

The rotational temperature of a low energy (0.09 eV), C-2 Swan band state (a (3)Pi u), obtained by white light absorption, is compared to the rotational temperatures of three electronic excited states [C-2(d (3)Pi g),CH(A(2)Delta) and CN(B (2)Sigma(+))] in a high power, H-2/CH4 microwave plasma used for diamond deposition. All temperatures are measured at 50 mbar, and both continuous (as a function of microwave power) and pulsed (as a function of time after the pulse) modes of operation are investigated. The rotational temperature of C-2's excited state is found to be higher than that of the low energy state (assumed equal to the gas temperature), indicating that the excitation of C-2 is to a large extent the result of chemical reactions (chemiluminescence) rather than electronic excitation. The rotational temperatures of CH(A (2)Delta) and CN(B (2)Sigma(+)) excited states are also higher than that for C-2's low energy state temperature. (C) 1999 American Institute of Physics. [S0021-8979(99)09320-2].