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) dissolved in cyclohexane are measured and analyzed to establish the existence of a (2)A(1) excited state that is nearly degenerate with the optically stronger, (2)A(2) excited state. The depolarization ratio of the symmetric stretch fundamental transition is measured at several excitation wavelengths spanning the lowest-energy electronic transition centered at similar to 360 nm. The depolarization ratio of this transition reaches a maximum value of 0.25+/-0.04 directly on resonance suggesting that scattered intensity is not derived from a single excited state. The depolarization ratios are modeled utilizing the time-dependent formalism for Raman scattering. This analysis demonstrates that the observed Raman depolarization ratios are derived from contributions of two excited states of (2)A(1) and (2)A(2) symmetry to the observed scattering. 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 state to the (2)A(1) surface. Both the role of the (2)A(1) state in the photochemistry of OClO and the importance of this state in modeling resonance Raman intensities are discussed. (C) 1997 American Institute of Physics. [S0021-9606(97)02944-9].