HONO in solid Kr: Site-selective trans <-> cis isomerization with narrow-band infrared radiation

Narrow-band resonant IR radiation promotes trans <----> cis isomerization o f HONO in a Kr matrix when the O-H stretching or N=O first overtone modes a re excited. The isomerization process is selective with respect to matrix s ites, and the HONO concentrations in various matrix sites are unchanged, de monstrating the stability of the host cage under the resonant IR irradiatio n. The isomerization process is localized at the vibrationally excited mole cule and possesses a high quantum yield, possibly approaching 1 for the cis to trans reaction. The present experimental results on IR-induced isomeriz ation of HONO agree with the known molecular dynamics simulations. Our anha rmonic ab initio calculations describe well the vibrational properties of b oth HONO isomers, including a number of observed overtone and combination b ands. Especially remarkable in our opinion is the very good numerical agree ment between the calculated and experimental IR absorption cross sections f ound for all the fundamental modes. (C) 2000 American Institute of Physics. [S0021-9606(00)00933-8].