Photodissociation dynamics of IBr{sup -}(CO{sub 2}){sub n}, n<15

Journal Article · Tue Feb 01 04:00:00 EST 2005 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.1839178· OSTI ID:20662302

Sanford, Todd; Han, S -Y; Thompson, Matthew A; Parson, Robert; Lineberger, W Carl ^[1]

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1. JILA and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309 (United States)

We report the ionic photoproducts produced following photoexcitation of mass selected IBr{sup -}(CO{sub 2}){sub n}, n=0-14, cluster ions at 790 and 355 nm. These wavelengths provide single state excitation to two dissociative states, corresponding to the A{sup '} {sup 2}{pi}{sub 1/2} and B 2 {sup 2}{sigma}{sub 1/2}{sup +} states of the IBr{sup -} chromophore. Excitation of these states in IBr{sup -} leads to production of I{sup -}+Br and Br{sup -}+I{sup *}, respectively. Potential energy curves for the six lowest electronic states of IBr{sup -} are calculated, together with structures for IBr{sup -}(CO{sub 2}){sub n}, n=1-14. Translational energy release measurements on photodissociated IBr{sup -} determine the I-Br{sup -} bond strength to be 1.10{+-}0.04 eV; related measurements characterize the A{sup '} {sup 2}{pi}{sub 1/2}(leftarrow)X {sup 2}{sigma}{sub 1/2}{sup +} absorption band. Photodissociation product distributions are measured as a function of cluster size following excitation to the A{sup '} {sup 2}{pi}{sub 1/2} and B 2 {sup 2}{sigma}{sub 1/2}{sup +} states. The solvent is shown to drive processes such as spin-orbit relaxation, charge transfer, recombination, and vibrational relaxation on the ground electronic state. Following excitation to the A{sup '} {sup 2}{pi}{sub 1/2} electronic state, IBr{sup -}(CO{sub 2}){sub n} exhibits size-dependent cage fractions remarkably similar to those observed for I{sub 2}{sup -}(CO{sub 2}){sub n}. In contrast, excitation to the B 2 {sup 2}{sigma}{sub 1/2}{sup +} state shows extensive trapping in excited states that dominates the recombination behavior for all cluster sizes we investigated. Finally, a pump-probe experiment on IBr{sup -}(CO{sub 2}){sub 8} determines the time required for recombination on the ground state following excitation to the A{sup '} state. While the photofragmentation experiments establish 100% recombination in the ground electronic state for this and larger IBr{sup -} cluster ions, the time required for recombination is found to be {approx}5 ns, some three orders of magnitude longer than observed for the analogous I{sub 2}{sup -} cluster ion. Comparisons are made with similar experiments carried out on I{sub 2}{sup -}(CO{sub 2}){sub n} and ICl{sup -}(CO{sub 2}){sub n} cluster ions.

• OSTI ID: 20662302
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 5 Vol. 122; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ANIONS
BROMINE COMPOUNDS
BROMINE IONS
CHARGE EXCHANGE
ENERGY TRANSFER
EXCITATION
EXCITED STATES
GROUND STATES
IODINE COMPOUNDS
IODINE IONS
ION PAIRS
MILLI EV RANGE
MOLECULAR CLUSTERS
PHOTON-MOLECULE COLLISIONS
RECOMBINATION
SOLVENTS