Elementary Reactions of NH(a¹Δ) with Saturated Hydrocarbons in the Gas Phase

Abstract

The elementary reaction of NH(a1Δ) with the saturated hydrocarbons: was studied for R = CH4, C2H6, C3,H8, and n‐C4H10 at room temperature in the gas phase at low pressure (10 < p/mbar ≤ 40). NH(a) was produced by HN3 laser photolysis (λL = 248 nm) and detected by laser induced fluorescence. Time resolution was obtained from the variable delay between the photolysis pulse and the detecting laser pulse. – The rate constants (in cm3/mol s) were found to be: independent of pressure in the above given range. – The product NH2(X̃) and the quenching pathway (NH(X)) were followed directly and quantitatively by laser induced fluorescence. The quenching pathway was found to be unimportant([NH(X)]α /[NH(a)]0 < 1%) for all alkanes. The fraction of NH2(X̃) formed, {[NH2(X̃)]α/[NH(a)]0} decreases with increasing chain length from (CH4) = 1.0; (C2H6) = (0.34 ± 0.06); C3H8 = (0.20 ± 0.02) to n‐C4H10 = (0.07 ± 0.02). These ratios did not change with pressure (10 ≤ p/mbar ≤ 40). – The increase in the rate constants for the reactions with H–(CH2)n – H with increasing n (1 ≤ n ≤ 4) and the decrease in the NH2 yield demonstrate that NH2 is not formed by abstraction but by an insertion mechanism.