Ultrafast Experiments on the Photodissociation, Recombination, and Vibrational Relaxation of I2-: Role of Solvent-Induced Solute Charge Flow

Abstract

This paper describes extensive new ultrafast pump-probe experiments on the photodissociation, geminate recombination, and vibrational relaxation of 12-in various solvents with various counterions. The first measurements on 12-in polar aprotic solvents and in relatively nonpolar solvents are described. Recombination to the 3/2g(2113/2,s) excited state of 12-in solution and the 3/2g(2113/2,g) -3/2u(2113/2,u) transition in solution are assigned for the first time. The new analysis confirms the existence of an extremely rapid (0.3 ps) initial vibrational relaxation component corresponding to a major fraction of the ground-state relaxation ( 2 50% for water), followed by a slower solvent-dependent process on the 3-6 ps time scale. The experimental results herein are compared to the molecular dynamics simulations of 12-that are described in the companion article. The comparison to the simulations reveals that (i) the nonexponential vibrational relaxation dynamics should be attributed to solvent-induced 12-charge flow, and (ii) the Franck-Condon analysis used to analyze the experimental results herein may be inaccurate at high excess energy, owing to charge-transfer contributions to the spectrum.

Excited-State Dynamics of Chlorine Dioxide in the Condensed Phase from Resonance Raman Intensities

“…77 Studies on the vibrational relaxation of charged species in polar solvents have also demonstrated that dipole-dipole and charge-dipole interactions can dramatically affect the course of chemical reactions in solution. [78][79][80][81][82][83][84] However, nonpolar solvation dynamics must dominate the response of cyclohexane to OClO photoexcitation. The dynamics relevant to nonpolar solvation can be partitioned into two parts, a dielectric interaction involving dipole-induced dipole and induced dipole-induced dipole (i.e., van der Waals) coupling and mechanical forces representing the solvent response to the Comparison of the plots demonstrates that in the gas phase, significant evolution along the asymmetric stretch occurs upon photoexcitation; however, little evolution along this coordinate occurs in solution.…”

Simulation of UV photodissociation of I2−(CO2)n: Spin-orbit quenching via solvent mediated electron transfer

“…In particular, I 2 Ϫ has been studied in a wide variety of environments, including gas phase clusters, [3][4][5][6][7][8][9][10][11][12] liquid solutions, [13][14][15][16][17][18][19][20][21] and gas-surface collisions, [22][23][24][25] and these experiments have stimulated a variety of theoretical studies. These solvated molecular ions differ considerably from their neutral counterparts, since the interaction between the ion and the surrounding solvent, which can be as strong as the chemical bonding forces within the solute, depends sensitively on the solute charge distribution.…”

Vibrational relaxation of I2 in complexing solvents: The role of solvent–solute attractive forces

“…13,14 High-frequency oscillators ͑e.g., CvO͒ sample multiple solvent events and the combined coupling of inter-and intramolecular motions, and consequently tend to have much slower relaxation rates. 17 The edge of most solvent response functions falls around 200 cm Ϫ1 , and the relaxation rate of I 2 is accordingly quite solvent sensitive, ranging from a few picoseconds in interacting solvents like mesitylene to ϳ35 picoseconds in carbon tetrachloride.…”