Studies of chemical reactivity in the condensed phase. I. The dynamics of iodine photodissociation and recombination on a picosecond time scale and comparison to theories for chemical reactions in solution

Journal Article · Tue Jan 14 23:00:00 EST 1986 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.450578· OSTI ID:6464645

Harris, A L; Berg, M; Harris, C B

Picosecond transient absorption measurements from 1000--295 nm are used to monitor the recombination dynamics of iodine after photodissociation in a variety of inert solvents. The high time resolution and signal-to-noise ratio of these measurements permits the development of a detailed model of this reaction, which should resolve disagreements over the time scales of geminate recombination and vibrational relaxation and over the role of excited electronic state trapping. Most of the atoms which undergo geminate recombination do so in < or =15 ps, in agreement with the predictions of existing molecular dynamics simulations. The subsequent vibrational and electronic energy relaxation of the recombined molecule is relatively slow and accounts for most of the transient absorption dynamics. The relaxing X-state vibrational population distribution is extracted with an approximate method using calculated spectra of the excited vibrational levels and is compared to recent models. Vibrational relaxation times vary from approx.15 ps near the middle of the ground state well to approx.150 ps for complete relaxation to v = 0. The vibrational relaxation rates do not provide support for the predicted role of resonant vibration-to-vibration energy transfer to chlorinated methane solvents, but some evidence for this mechanism is found in alkane solvents. B-state predissociation times of 10--15 ps and A'-state lifetimes of 65--2700 ps are found depending on the solvent. Current theory is not able to satisfactorily explain the large variation of the A'-state lifetime in various solvents.

• Research Organization: Department of Chemistry, University of California, Berkeley, California 94720 and the Materials and Molecular Research Division, Lawrence Berkeley Laboratory, Berkeley, California 94720
• OSTI ID: 6464645
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 84:2; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical &amp; Physicochemical Properties
ABSORPTION SPECTRA
ABSORPTION SPECTROSCOPY
ALKANES
CHEMICAL REACTIONS
CHLORINATED ALIPHATIC HYDROCARBONS
DECOMPOSITION
DISPERSIONS
DISSOCIATION
ELEMENTS
HALOGENATED ALIPHATIC HYDROCARBONS
HALOGENS
HYDROCARBONS
IODINE
MIXTURES
NONMETALS
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RECOMBINATION
SOLUTIONS
SPECTRA
SPECTROSCOPY