Absolute rate coefficients of the reactions of CF2(ã 3B1) with C3H8, C3H6, iso-C4H8 and C3H4 between 295 and 550 K

Abstract

The rate coefficients of the removal of metastable electronically excited CF₂(ã ³B₁) by several hydrocarbons have been determined for the first time over an extended temperature range (295 K–550 K). CF₂(³B₁) radicals were generated by pulsed laser photolysis of C₂F₄ at 193 nm and real-time pseudo-first-order decays of the relative CF₂(³B₁) concentration were obtained by monitoring the CF₂(³B₁ → ¹A₁) emission at 570–700 nm. Over the experimental temperature range, the rate coefficients of CF₂(ã ³B₁) removal by (di-)alkenes exhibited a marked negative temperature dependence: k_C3H6(T) = (7.8 ± 2.3) × 10⁻¹³exp[+(500 ± 100)K/T] cm³ s⁻¹ molecule⁻¹, k_iso-C4H8(T) = (1.4 ± 0.2) × 10⁻¹²exp[+(762 ± 36)K/T] cm³ s⁻¹ molecule⁻¹, k_C3H4(T) = (2.1 ± 0.5) × 10⁻¹³exp[+(790 ± 83)K/T] cm³ s⁻¹ molecule⁻¹. For the removal of CF₂(ã ³B₁) by C₃H₈, the rate coefficient exhibited a small positive temperature dependence: k_C3H8(T) = (6.5 ± 2.2) × 10⁻¹³exp[−(252 ± 130)K/T] cm³ s⁻¹ molecule⁻¹.