Internal energy distributions from nitrogen dioxide fluorescence. 2. Collisional energy transfer from excited nitrogen dioxide

Abstract

We follow the collisional deactivation of laser-excited nitrogen dioxide through its dispersed fluorescence. The energy acceptor gases are NO[sub 2] at four excitation energies ranging from 18828 to 24989 cm[sup [minus]1] and five monatomic gases, four diatomic gases, and three polyatomic gases with 18828-cm[sup [minus]1] excitation energy. The nominal products are the shapes of the internal energy distributions, which are obtained and plotted for several representative cases. From these distributions, the first three moments of the internal energy distributions are derived as a function of molecular collisions and tabulated as (i) the average internal energy, (ii) energy spread, and (iii) skewness. These quantities are plotted against c(M)t, the product of buffer gas concentration c(M) and delay time after laser excitation t(0.5-2 [mu]s), which is a quantity proportional to number of collisions. The negative slope of average energy vs c(M)t is the macroscopic energy-transfer rate constant, k[sub [epsilon]](M). Average energies (E) for all NO[sub 2]-buffered data taken at four excitation wavelengths are well represented by the single equation, fourth order in energy: d(E)/d(c[sub NO(2)]t) = [minus]k[sub 4](E)[sup 4], where k[sub 4] = 8.06 [times] 10[sup [minus]25] (cm[sup 3])[sub energy] molecule[sup [minus]1] cm[sup 3] s[sup [minus]1]. 32 refs., 16 figs., 7 tabs.