Simulation study of solvent shifts of vibrational overtone spectra

Abstract

Buckingham's theory of the solvent shift of vibrational spectral frequencies predicts that the shift of the v = 0 → n overtone transition is n times the shift of the fundamental v = 0 → 1. We test this prediction by molecular dynamics simulations using existing intermolecular potential models for liquid N₂ and dilute N₂ in liquid Ar, at standard state conditions. We extend Buckingham's theory by including additional intramolecular potential and perturbation terms which lead to solvent-induced anharmonicity, i.e. O(n ²) terms in the solvent shift. The simulations show that Buckingham's prediction is not accurate for N₂ at standard liquid state conditions. We find that at these conditions there is a significant positive O(n ²) contribution to the solvent shifts and that for n ∼ 20 the shifts change sign from red to blue. Simulation results and indirect evidence from shock wave experiments with liquid N₂ show that Buckingham's prediction is more accurate for high-pressure high-temperature conditions, where the shifts are blue and only slightly nonlinear in n.

Notes

e-mail: [email protected] (SG)

e-mail: [email protected] (IST)

e-mail: [email protected] (IST)

e-mail: [email protected] (CGG)

Additional information

Notes on contributors

C. G. Gray ¶

e-mail: [email protected] (SG) e-mail: [email protected] (IST) e-mail: [email protected] (CGG)