Abstract
Acrolein (C2H3CHO) is a resistant to photooxidation and a day- and night- time lachrymator found in Los Angeles smog. We investigate photodissociation dynamics of acrolein by detecting fragment HCO. The formation threshold of acrolein to C2H3+HCO is measured to be 298±1 nm estimated from relative yield of HCO vs. photolysis wavelength. Florescent spectra 2A¢? 2A¢ (0,0) of HCO were detected; the intensity is corrected for both the florescent quantum yield and the effect of axis switching to obtain the population of rotational states of HCO. Rotational states up to N = 12 and Ka = 2 of HCO were populates and the population distribution can be described according to a Boltzmann distribution at temperature 89 ± 5 K. The relative rotational population of HCO dissociated from acrolein excited to the S1 state at photolysis energy 34 032 ± 1 cm-1 is obtained. The rotational energy of HCO is obtained to be ~34% of available energy. The population of Ka=1 doublet states and is about equally populated unlike the case of acetaldehyde. The population distribution among the rotational states of HCO indicates that a relatively loose transition state for formation of C2H3+HCO. The appearance rate of HCO is measured to be faster than our experimental condition 2’108 s-1. The Boltzmann-type distribution and small available obtained in this work energy indicate that fragmentation occurs through a surface with barrierless or an exit barrier less than 250 cm-1. Our experiment results imply that radical products can be either dissociated from the S1 or T1 surface.