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

Abstract

Resonance Raman spectra of chlorine dioxide (OClO) dissolved in cyclohexane obtained with excitation throughout the 2 B 1 -2 A 2 electronic transition are presented. Resonance Raman intensity corresponding to all vibrational degrees of freedom (the symmetric stretch, bend, and asymmetric stretch) is observed, demonstrating that excited-state structural evolution along all three coordinates occurs upon photoexcitation. The electronic absorption and absolute resonance Raman cross sections are reproduced employing the time-dependent formalism for Raman scattering using an anharmonic description of the 2 A 2 , excited-state potential-energy surface. Analysis of the resonance Raman cross-sections demonstrates that both homogeneous and inhomogeneous broadening mechanisms are operative in cyclohexane. Comparison of the experimentally determined, gas-phase 2 A 2 surface to that in solution defined by the analysis presented here shows that although displacements along the symmetric stretch and bend are similar in both phases, evolution along the asymmetric stretch is dramatically altered in solution. Specifically, employing the gas-phase potential along this coordinate, the predicted intensity of the overtone transition is an order of magnitude larger than that observed. The analysis presented here demonstrates that the asymmetric stretch overtone intensity is consistent with a reduction in excited-state frequency along this coordinate from 1100 to 750 ( 100 cm -1 . This comparison suggests that differences in evolution along the asymmetric stretch may be responsible for the phase-dependent reactivity of OClO. In particular, the absence of substantial evolution along the asymmetric stretch in solution results in the ground-state symmetry of OClO being maintained in the 2 A 2 excited state. The role of symmetry in defining the reaction coordinate and the nature of the solvent interaction responsible for modulation of the excited-state potential energy surface are discussed.

Kinetics and Mechanism of Catalytic Decomposition and Oxidation of Chlorine Dioxide by the Hypochlorite Ion

“…While this reaction is one of the possible fragmentation * To whom correspondence should be addressed. (1) channels in condensed-phase photolysis of chlorine dioxide, [22][23][24][25][26][27][28][29] it does not seem to be feasible in the thermally induced decomposition. In support of this statement, it should be remembered that slightly acidic solutions of chlorine dioxide can be stored in the dark without apparent concentration loss for several months.…”

Calculation of absorption and resonance Raman cross sections of ClO2 in the gas‐phase and in solution: including Duschinsky effects

“…Their work indicated that theà 2 A 2 state is predissociated through spin-orbit coupling of 2 A 1 state, and asymmetric stretch potential of 2 A 2 state does not show evidence of a double minimum as has been previously proposed. Esposito et al [8] have obtained the absorption and resonance Raman spectra of OClO dissolved in cyclohexane at resonance with the X 2 B 1 -à 2 A 2 electronic transition. The absorption and resonance Raman spectra of OClO at resonance with the X 2 B 1 -à 2 A 2 electronic transition in the gas-phase [11] and in the solvents such as water, [10] chloroform, [12] and cyclohexane [8] were obtained.…”

“…Esposito et al [8] have obtained the absorption and resonance Raman spectra of OClO dissolved in cyclohexane at resonance with the X 2 B 1 -Ã 2 A 2 electronic transition. The absorption and resonance Raman spectra of OClO at resonance with the X 2 B 1 -Ã 2 A 2 electronic transition in the gas-phase [11] and in the solvents such as water, [10] chloroform, [12] and cyclohexane [8] were obtained. For analysis of resonance Raman intensities, the excited-state potential energy surfaces were modeled as harmonic for both symmetric bending and asymmetric stretch coordinates, and cubic anharmonic for the symmetric stretch coordinate.…”

“…Experimental absorption spectrum of OClO in cyclohexane (Reference[8]) solid curve and the calculated spectrum for displaceddistorted-rotated (dashed curve) harmonic oscillator model using the parameters ofTables 3 and 4.…”

“…Experimental (Reference[8]) and calculated resonance Raman excitation profile of the symmetric stretch fundamental (a) and overtone (b) for OClO in cyclohexane. Calculations were performed using parameters of…”