Analysis of depolarization ratios of ClNO_2 dissolved in methanol

摘要

A detailed analysis of the resonance Raman depolarization ratio dispersion curve for the N–O symmetric stretch of nitryl chloride in methanol at excitation wavelengths spanning the D absorption band is presented. The depolarization ratios are modeled using the time-dependent formalism for Raman scattering with contributions from two excited states (2~1A_1 and 3~1B_1), which are taken as linearly dissociative along the Cl–N coordinate. The analysis focuses on the interplay between different types of broadening revealing the importance of inhomogenous broadening in determining the relative contributions of the two electronic transitions.We find that the transition dipole moment (M) for 2~1A_1 is greater than for 3~1B_1, in agreement with gas phase calculations in the literature [A. Lesar, M. Hdoscek, M. Muhlhauser, and S. D. Peyerimhoff, Chem. Phys. Lett. 383, 84 (2004)]. However, we find that the polarity of the solvent influences the excited state energetics, leading to a reversal in the ordering of these two states with 3~1B_1 shifting to lower energies. Molecular dynamics simulations along with linear response and ab initio calculations support the evidence extracted from resonance Raman intensity analysis, providing insights on ClNO_2 electronic structure, solvation effects in methanol, and the source of broadening, emphasizing the importance of a contribution from inhomogeneous linewidth.