title: Reaction Dynamics of CN Radicals in Acetonitrile Solutions.
abstract: The bimolecular reactions that follow 267 nm ultraviolet photolysis of ICN in acetonitrile solution have been studied using transient absorption spectroscopy on the picosecond time scale. Time-resolved electronic absorption spectroscopy (TEAS) in the ultraviolet and visible spectral regions observes rapid production and loss (with a decay time constant of 0.6 ± 0.1 ps) of the photolytically generated free CN radicals. Some of these radicals convert to a solvated form which decays with a lifetime of 8.5 ± 2.1 ps. Time-resolved vibrational absorption spectroscopy (TVAS) reveals that the free and solvated CN-radicals undergo geminate recombination with I atoms to make ICN and INC, H atom abstraction reactions, and addition reactions to solvent molecules to make C3H3N2 radical species. These radical products have a characteristic absorption band at 2036 cm(-1) that shifts to 2010 cm(-1) when ICN is photolyzed in CD3CN. The HCN yield is low, suggesting the addition pathway competes effectively with H atom abstraction from CH3CN, but the delayed growth of the C3H3N2 radical band is best described by reaction of solvated CN radicals through an unobserved intermediate species. Addition of methanol or tetrahydrofuran as a cosolute promotes H atom abstraction reactions that produce vibrationally hot HCN. The combination of TEAS and TVAS measurements shows that the rate-limiting process for production of ground-state HCN is vibrational cooling, the rate of which is accelerated by the presence of methanol or tetrahydrofuran.
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Koyama
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
authors.forename: Philip
authors.initials: P
authors.lastname: Coulter
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Grubb
authors.affiliation: Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory , Harwell Oxford, Didcot, Oxfordshire OX11 0QX, U.K.
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Greetham
authors.affiliation: Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory , Harwell Oxford, Didcot, Oxfordshire OX11 0QX, U.K.
authors.forename: Ian P
authors.initials: IP
authors.lastname: Clark
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Orr-Ewing