The detection of CH 3CO, C 2H 5, and CH 3CHO by rempi/mass spectrometry and the application to the study of the reactions H+CH 3CO and O+CH 3CO

Abstract

The discharge flow reactor technique combined with molecular beam sampling and either resonance enhanced multi-photon ionization (REMPI)/mass spectrometry or low energy electron impact ionization (EI)/mass spectrometry has been used to study the specific and sensitive detection of radicals and molecules and the reaction of radicals with atoms. The acetyl radical CH 3 CO shows a REMPI mass spectrum at m/e =43 in the wavelength region 395–415 nm and at 430 nm. The ethyl radical C 2 H 5 is detected by multi-photon ionization at the wavelength 400–460 nm by the parent ion m/e =29. Acetyldehyde is monitored sensitively by a (2+1) Rydberg transition at 440.6 nm with ion fragmentation at m/e =15, 29, 43. The reaction mechanism of CH 3 CO radicals with H atoms at low pressure (0.01–0.1; 0.5–10 mbar) and temperature (293–300 K) is given by CH 3 CO+H→CH 3 +HCO (7a) →CH 3 CHO (7b) →CH 2 CO+H 2 (7c) Reaction channel (a) is the main route at low pressure (1 mbar) and the ratio of (a)/(b) is discussed in a model of chemical activation/collision stabilization. The rate constant k 1 was determined relative to the reaction C 2 H 5 +H leading to k 7 =(3.3+2)·10 13 cm 3 /mol· s The ratio of the rate constants of acetyl CD 3 CO and vinoxy CD 2 CHO radicals with D atoms was determined as k 7 dd (CD 3 CO+D)/ k 11− d (CD 2 CHO+D)=1.6+0.6 For the reaction CH 3 CO+O→CH 3 +CO 2 (12a) →OH+CH 2 CO (12b) the route (12a) dominates. The rate of this reaction (12) was measured using the reaction C 2 H 5 +O as a standard: k 12 =(1.2±0.4)·10 14 cm 3 /mol· s