Vibrational relaxation of NO(υ=1) by oxygen atoms

Abstract

The rate constant kO(υ=1) for NO(υ=1) vibrational relaxation by O has been measured at room temperature using a laser photolysis-laser probe technique. Vibrationally excited NO and relaxer O atoms were formed using 355 nm laser photolysis of a dilute mixture of NO2 in argon bath gas. The time evolution of both the NO(υ=1) and the O atoms was monitored using laser-induced fluorescence (LIF). The required absolute O-atom densities were obtained through a comparison of O-atom LIF signals from the photolysis source and from a titrated cw microwave source. At early times the O atoms constitute the most important loss mechanism for the nascently produced NO(υ=1). Possible effects from NO(υ=1) vibrational ladder-climbing and from thermal expansion have been shown to be minimal. The rate constant kO(υ=1)=(2.4±0.5)×10−11 cm3 s−1 determined herein is a factor of 2 to 3 lower than the generally accepted value of kO(υ=1) used in thermospheric modeling. The present value for kO(υ=1) is the same, within the error bars, as the kO(υ=2,3) previously measured in this laboratory using an entirely different technique, resonant infrared laser excitation of NO(υ=0). This result suggests that the collisional relaxation rates are independent of υ. A recent quasiclassical trajectory calculation, in which both allowed NO–O surfaces have been explicitly considered, predicts a collisional relaxation rate which is in good agreement with the present result. The kO(υ=1) value, along with previously measured rate constants for NO–O high-pressure recombination (krec∞) and isotope exchange (kiso), can serve as a proxy for the rate coefficient kC describing the formation of a long-lived NO2* intermediate from O+NO collisions. The present value for kO(υ=1) is significantly lower, however, than a recent determination of krec∞ and also the value of kC derived from kiso. In the latter case the comparison is not as straightforward.

A Theoretical Study of Rate Coefficients for the O + NO Vibrational Relaxation

“…The state-to-state rate coefficients and branching ratios are predicted to be nearly independent of the final vibrational state, which may suggest a strong statistical behavior of the title energy transfer process. Calculated state-to-all rate constants for room temperature were also found to be in good agreement with the reported experimental values, [13][14][15] albeit a factor of nearly 3 or so smaller than the recommended values of Fernando and Smith. 11 …”

“…As discussed above, the inclusion of long-range forces on the MBE form for the 2 A′′ state should not significantly alter the calculated vibrational relaxation rate constant. In fact, the corrected value for the V ) 1 f 0 transition, is now predicted to be k(T ) 298 K) ) 2.59 ( 0.58 × 10 -11 cm -3 s -1 , in even closer agreement with the Dodd et al 15 experimental value, and still far from the recommended 11 one.…”

“…Such a finding has been previously reported by Duff and Sharma 20 who noted that "the SAC model for NO(V e 1, 2) and the expectations of statistical theories predict that V′ ) 0 Thermal state-to-all rate constants as a function of the initial vibrational quantum number for the three different temperatures considered in this work. Also shown are experimental 11,12,14,15 and theoretical 19,20 data found in the literature.…”

3-D GCM modelling of thermospheric nitric oxide during the 2003 Halloween storm

“…A comprehensive mesosphere-thermosphere chemical scheme is included. Radiative cooling due to 5-µm emission from excited NO is calculated as described in Kockarts (1980), with a collisional deactivation rate of 2.4×10 −11 cm 3 s −1 (Dodd et al, 1999). The model has been presented in detail in Harris (2001) and Dobbin (2005).…”

Application of advanced laser diagnostics to hypersonic wind tunnels and combustion systems.

“…However, at higher pressures, reaction #52 could become important and reaction #47 may compete with V-V and V-T exchanges. In addition, the reverse of reaction #47, referred to as a chemical feed reaction in Dodd (1999), regenerates vibrationally excited NO, and would directly affect the vibrational decay of NO, as well as indirectly affect O 2 (and N 2 to a lesser degree).…”