Rate coefficients and production of vibrationally excited HCl from the reactions of chlorine atoms with methanol, ethanol, acetaldehyde and formaldehyde

Abstract

Room temperature rate coefficients have been determined for the reactions of Cl (²P_3/2) atoms with methanol, ethanol, formaldehyde and acetaldehyde. Cl atoms were produced by laser flash photolysis of molecular chlorine, in the presence of oxygen to prevent chain chemistry. IR emission from vibrationally excited HCl was observed for all reagents. For the reactions with methanol and acetaldehyde the kinetics have been determined by both IR diode laser absorption spectroscopy (k_Cl+CH3OH = (5.83 ± 0.77) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹k_Cl+CH3CHO = (7.7 ± 1.1) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹) and IR chemiluminescence (k_Cl+CH3OH = (5.38 ± 0.25) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, k_Cl+CH3CHO = (8.8 ± 1.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. For ethanol and formaldehyde IR chemiluminescence measurements gave k_Cl+HCHO = (6.98 ± 0.69) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k_Cl+C2H5OH = (1.02 ± 0.19) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. The fraction of vibrationally excited HCl was determined relative to that of acetaldehyde and when put on an absolute scale the values for methanol, ethanol and formaldehyde were: 0.25 ± 0.04, 0.21 ± 0.03 and 0.91 ± 0.14 respectively.