Journal of Chemical Physics, Vol.117, No.20, 9266-9274, 2002
The 212.8-nm photodissociation of formic acid: Degenerate four-wave mixing spectroscopy of the nascent OH(X (2)Pi(i)) radicals
The 212.8-nm photodissociation dynamics of formic acid was investigated utilizing degenerate four-wave mixing spectroscopy. The background-free rotational spectrum of the nascent OH radicals was obtained, and a cold rotational energy distribution peaking at N"=3 was extracted from the DFWM spectrum. The distribution was well approximated by a Boltzmann distribution with a rotational temperature of T(rot)similar to716 K, which corresponds to an average rotational energy of similar to498 cm(-1). The observation of a nonstatistical spin-orbit state distribution, with a preference for the low-energy F-1 manifold, implies the absence of any interactions with nearby triplet states during dissociation. Preferential population of the Lambda-doublet was observed, indicating that the nu(7) H-O-C bending vibration in HCOOH((A) over tilde) and the recoil impulse are the principal sources of the OH rotation.