Spectroscopic studies of low-pressure flames III. Effective rotational temperatures and excitation mechanism for C 2 bands

Abstract

Intensity measurements on the Swan bands of C 2 give effective rotational temperatures for a number of flames. For oxygen/acetylene at 1 atm. the value is 4950° K, falling to 3800° K at 2 mm. For acetylene/air it is 3400° K at 1 atm., falling a little at low pressure. In discussing the excitation process, reasons are given against its being a true chemiluminescence. It is believed that the C 2 radicals are formed with high rotational energy and are electronically excited by collision with energy-rich molecules present in the flame and responsible for the high excitation temperatures previously recorded. These energy-rich molecules probably possess excess vibrational energy.