GENERATION AND 355 NM LASER PHOTODISSOCIATION OF NITROUS-ACID (HONO) AND HONO-WATER CLUSTERS

A stable source for the continuous production of high concentrations o f gaseous nitrous acid (HONO) up to 5000 ppm has been developed, chara cterized, and employed for a study of the near-UV photodissociation of HONO and HONO-water clusters in a continuous supersonic free-jet expa nsion. The source consists of a flow reactor fed with aqueous reagent solutions purged by an inert carrier gas at flow rates up to 1 L/min. The dynamics of the photodissociation of jet-cooled HONO and HONO-wate r clusters at 355 nm have been studied by measuring the rotational dis tribution of the nascent NO (upsilon''=2) photofragment using the lase r-induced fluorescence (LIF) technique. Distinctly bimodal rotational distributions have been observed for the nascent, vibrationally excite d NO, which are well described by the sum of two components: a Gaussia n distribution at high J and a 170 K Boltzmann distribution in the low -J range reflecting photodissociation of bare HONO, HONO-H2O complexes , and small HONO water clusters.