Infrared photodissociation spectra of isomeric SiOH+-Ar-n (n=1-10) complexes

Infrared photodissociation spectra of mass-selected SiOH+-Ar-n complexes (n = 1-10) have been recorded in the vicinity of the OH stretch (nu(l)) vibra tion of SiOH+. The SiOH+-Ar dimer has also been investigated by ab initio c alculations at the MP2 level and two stable isomers have been found. The li near proton-bound global minimum (D-e = 1117 cm(-1)) and the less stable T- shaped silicon-bound geometry (D-e = 938 cm(-1)) are separated by an isomer ization barrier of similar to 500 cm(-1) Three rotationally resolved bands observed in the dimer spectrum are assigned to the nu(l) fundamental (3444. 9 cm(-1)) and the nu(l) + nu(s) (3554.6 cm(-1)) and nu(l) + 2 nu(b) (3581.5 cm(-1)) combination bands of the linear isomer, whereas a weak unresolved band centered at 3673 cm(-1) is attributed to the nu(l) fundamental of the T-shaped isomer. The assignments are based on the rotational analysis, vibr ational frequencies and comparison with the ab initio results. Systematic n u(l) vibrational band shifts observed in the spectra of larger clusters hav e allowed to monitor the cluster growth and identify coexisting isomers. (C ) 1998 Elsevier Science B.V. All rights reserved.