EVIDENCE FOR THE B-2(1)-(2)A(1) ELECTRONIC-TRANSITION IN CHLORINE DIOXIDE FROM RESONANCE RAMAN DEPOLARIZATION RATIOS

The resonance Raman depolarization ratios of chlorine dioxide (OClO) d issolved in cyclohexane are measured and analyzed to establish the exi stence of a (2)A(1) excited state that is nearly degenerate with the o ptically stronger, (2)A(2) excited state. The depolarization ratio of the symmetric stretch fundamental transition is measured at several ex citation wavelengths spanning the lowest-energy electronic transition centered at similar to 360 nm. The depolarization ratio of this transi tion reaches a maximum value of 0.25+/-0.04 directly on resonance sugg esting that scattered intensity is not derived from a single excited s tate. The depolarization ratios are modeled utilizing the time-depende nt formalism for Raman scattering. This analysis demonstrates that the observed Raman depolarization ratios are derived from contributions o f two excited states of (2)A(1) and (2)A(2) symmetry to the observed s cattering. The results presented here support the emerging picture of OClO excited-state reaction dynamics in which photoexcitation to the ( 2)A(2) excited state is followed by internal conversion from this stat e to the (2)A(1) surface. Both the role of the (2)A(1) state in the ph otochemistry of OClO and the importance of this state in modeling reso nance Raman intensities are discussed. (C) 1997 American Institute of Physics. [S0021-9606(97)02944-9].