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Issue 12, 2001
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Vibrational excitation and caging following the photodissociation of small HBr clusters in and on large Ar clusters

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Abstract

The photodissociation of a small (HBr)x cluster adsorbed on or embedded in larger Arn clusters has been studied at 243 nm. We measured the kinetic energy distribution of the H atom products in a time-of-flight mass spectrometer using (2 + 1)-resonance-enhanced multiphoton ionization (REMPI) spectroscopy. This observable provides information both on the amount of caged H atoms with zero velocity and on the vibrational excitation of HBr molecules in the cluster which have undergone a collision with unperturbed fast, already dissociated H atoms. In the surface case, generated by the pick-up technique, (HBr)x clusters from x = 1 to 4 were investigated on Arn clusters with 〈n〉 = 139. While the ratio of caged to uncaged atoms Rc is about 2, similar to the result for surface adsorbed monomers, the vibrational excitation is accompanied by rotational excitation. It is mainly attributed to the constrained geometry of surface adsorbed (HBr)2 dimers. In the embedded case, the (HBr)x clusters of 〈x〉 = 8 were investigated in Arn clusters of variable size from 〈n〉 = 100 to 12. Here, the amount of caged to uncaged atoms varies drastically, by a factor of 50, as a function of the argon cluster size. In the inelastic collisions, well resolved peaks were observed for the vibrational excitation into [italic v (to differentiate from Times ital nu)] = 1 and [italic v (to differentiate from Times ital nu)] = 2.

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Publication details

The article was received on 11 Dec 2000, accepted on 06 Feb 2001 and first published on 07 Mar 2001


Article type: Paper
DOI: 10.1039/B009878G
Citation: Phys. Chem. Chem. Phys., 2001,3, 2372-2377
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    Vibrational excitation and caging following the photodissociation of small HBr clusters in and on large Ar clusters

    R. Baumfalk, N. Hendrik Nahler and U. Buck, Phys. Chem. Chem. Phys., 2001, 3, 2372
    DOI: 10.1039/B009878G

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