Temperature measurements of C 2 and CN radicals generated in a shock tube, I. Pyrolysis in the absence of oxygen

Abstract

The excitation tem peratures of C 2 and CN radicals generated in a shock tu b e by the pyrolysis of cyanogen and acetylene have been measured in the range 3000 to 5000 °K by a brightness and emissivity method. The experimental measurements were made with photomultipliers whose outputs were recorded on a cathode ray oscillograph, so that complete histories of the temperature could be obtained. The radicals showed a radiative relaxation zone at the front followed by a period of constant temperature whose value agreed well with the results of calculations. These allowed for the species C 2 H 2 , C 2 H , C 3 , C 2 , C, CH, H 2 and H from acetylene and CN, C 3 , C 2 , C ,N 2 , and N from cyanogen. The reaction 2CN → C 2 + N 2 is discussed and found to have an activation energy of 96 kcal/mole. The processes leading to the formation of the electronically excited radicals are discussed with reference to the radiative relaxation at the shock front.