화학공학소재연구정보센터
Journal of Chemical Physics, Vol.113, No.5, 1891-1897, 2000
Photodissociation of formic acid
The photodissociation of formic acid has been studied experimentally and theoretically. Ab initio calculations were performed to study the dissociative profiles of five reaction channels on the S-0, S-1, and T-1 potential energy surfaces. The vibrationally excited nascent products were detected using a time-resolved Fourier transform infrared spectrometer after laser photolysis at 248 or 193 nm. In the 248 nm photolysis, the HCOOH molecule was first excited to the S-1 state, but it was found that the dissociation takes place on the S-0 surface after internal conversion. The products of the vibrationally excited CO, CO2(v(3)) and H2O(v(1)) were detected. During the dissociation process the vibrationally energized molecule is geometrically memorized and dynamically controlled, with the yield preference of CO and H2O over that of CO2 and H-2. The ratio of CO(v greater than or equal to 1)/CO2(v greater than or equal to 1) is estimated as < 7.5. Vibrationally excited CO (v) and CO2(v(3)) are also found in the 193 nm photolysis but the CO/CO2 ratio increases to 11. Most of the dissociation is thought to occur on the S-0 state. At this wavelength another dissociation channel which produces OH and HCO radicals on S-1 surface has been identified. The dissociation is unlikely to occur on the T-1 surface, as the energy barriers are fairly high.