Vibronic interactions, resonance Raman spectra and bond strengths for the radical anion salts of tetracyanoethylene

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Abstract
Raman spectra for the intensely colored salts of the tetracyanoethylene radical anion with sodium and potassium cations confirm previous assertions that the infrared salt spectra are completely dominated by vibronic interaction effects. As expected, strong Raman scattering has been observed at frequencies coincident with the intense infrared bands which have been assigned to totally symmetric modes activated by an ``electron‐vibration'' moment. The scattering intensities of the symmetric stretching modes (ν1, ν2, and ν3) reveal a complex dependence on excitation frequency which is qualitatively consistent with the observed vibronic structure of the electronic absorption band. By confirming the assignment of several of the radical anion internal modes, the Raman data have also permitted the evaluation of reliable stretching constants for comparison with the neutral molecule force constants and quantum chemical predictions of bond order changes. New data and a subsequent force constant analysis have required the reassignment of