Temperature and Wavelength Dependence of the Thermal Emission and O–NO Recombination Spectra of NO2

Abstract

The thermal emission spectrum of shock-heated NO2 has been measured from 4000 to 9500 Å at 2000°K. The bulk of the emission lies in the near infrared rather than in the visible. NO2 is at least 15 times as efficient as Ar in quenching NO2* due to the step NO2*+NO2→NO+NO3, k≈(9×108) T½ liter mole−1·sec−1. N2 as diluent behaves like a monatomic gas (Ar) at a translational temperature corresponding to rotational but not vibrational relaxation behind the front; the excitation is uncoupled to the rotational and vibrational temperature of N2. The radiative lifetime of NO2 is approximately equal to 10−7 sec. In systems containing O, NO, and NO2 the total emission can be resolved into contributions from thermal and recombination emissions; combining literature values the ``rate'' for O+NO→NO2+hv can be written (1.1×1011) T−1.59 exp (670/RT) cc mole−1·sec−1. Thermal and recombination contributions to the equilibrium emissivity of hot air are estimated.