Abstract
A theoretical analysis of the temperature and pressure dependence of the reaction HO + NO~2~ + M ⇔︁ HONO~2~ + M is made over the temperature range 50–1400 K and the pressure range 10^−4^–10^3^ bar where experimental data are available. The treatment accounts for contributions from anharmonicity, centrifugal barriers, angular momentum couplings, and weak collisions. It is shown that broadening factors F(x), with log F(x) ≈ [1 + (log x/N)^2^]^−1^ log F~c~, x = k~1,0~/k~1,∞~, N ≈ 0.75 – 1.27 log F~c~ (where log = log~10~), and F~c~ = 0.40 (±0.02), well represent the calculated falloff curves in the experimental range. Values of k~1,0~ = [N~2~] 3.0 × 10^−30^ (T/300 K)^−3.0^ cm^6^ molecule^−2^ s^−1^ and k~1,∞~ = 3.6 × 10^−11^ cm^3^ molecule^−1^ s^−1^, are consistent with experiments over the range 220–400 K. The NASA/JPL policy of using F~c~ = 0.6 and N = 1 leads to apparent values of k~1,0~, and k~1,∞~ which are too low, although experimentally observed parts of the falloff curves can well be reproduced. The IUPAC recommendation of a temperature dependence of F~c~ ≈ exp(−T/T~c~) should also be abandoned because F~c~ is nearly temperature independent between 50 and 1400 K. The analysis of experimental limiting low pressure rate coefficients k~1,0~ leads to apparent average energies 〈ΔE〉 transferred per collision of about −160 cm^−1^ for M = N~2~, and −80 cm^−1^ for M = Ar, which are nearly temperature independent over the range 200–400 K for M = N~2~, and only weakly temperature dependent between 300 and 1400 K for M = Ar. The analysis of k~1,0~, which leads to 〈ΔE〉, and of k~1,∞~, however, are markedly influenced by the lack of sufficiently precise information on the interaction potential between HO and NO~2~. For this reason, the consequences of uncertainties are discussed in detail. Possible contributions of HOONO isomer formation in the reaction are also discussed. It is shown that HOONO yields, at pressures below 1 bar, most probably are smaller than about 2.5% while yields up to 20% are possible at 100 bar. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 878–889, 2001