We have investigated the dissociation dynamics of the ArNO van der Waals molecule near 225 nm. This photon energy excites ArNO as much as 400 cm -1 above the photodissociation threshold, producing Ar + NO(A 2 Σ + ,V)0,N)0-12). In the first series of experiments, we deduce the population of rotational levels produced in NO(A) during photodissociation of ArNO with resonance enhanced multiphoton spectroscopy (REMPI) through the E-state. The rotational state distributions show anomalous nonstatistical behavior peaking near high N states. This behavior is consistent with the rotational rainbow effects observed by others with the maximum rotational quantum number proportional to the square root of the available energy. In the second experiments, 225 nm photons sequentially dissociate ArNO and then nonresonantly ionize the NO(A) products, which we observe using velocity-mapped ion imaging. The ion images display rings corresponding to the production of different rotational states of NO(A) during dissociation. We measure the appearance threshold for products from dissociation of ArNO to produce NO(A,N)0) as 44291 ( 2 cm -1 . Finally, we observe the contribution of hot bands to the rotational state distribution.

Nitromethane (CH(3)NO(2)) and its chlorinated analogue, chloropicrin (CCl(3)NO(2)), were photolyzed at 193, 248, and 266 nm, and the products were observed by time-dependent Fourier transform infrared emission spectroscopy. At 193 and 248 nm, the primary photodissociation pathway for nitromethane was cleavage of the C-N bond to produce CH(3) + NO(2)(A (2)B(2)). At 266 nm, weak emission was observed following photodissociation of nitromethane, but an infrared spectrum could not be obtained. The photodissociation of chloropicrin at 193 nm produced the analogous product channel CCl(3) + NO(2)(A (2)B(2)) in addition to several other product channels. At 248 and 266 nm, only CCl(3) + NO(2)(A (2)B(2)) was observed. The production of phosgene (CCl(2)O) from chloropicrin photodissociation was not observed in this study.