Inhomogeneous broadening, dephasing, and interference effects in multidimensional vibrational spectroscopy.

摘要

Qualitative and semiquantitative simulation techniques were applied to common infrared four wave mixing (IRFWM) processes that contribute to the output signals of multiresonant vibrational spectroscopies. Distinct features of the nonresonant background (NRB), coherent antiStokes Raman (CARS), singly vibrationally enhanced (SIVE), doubly vibrationally enhanced infrared (DOVE-IR), doubly vibrationally enhanced Raman (DOVE-Raman), and triply vibrationally enhanced (total vibrational resonance by third laser enhancement of DOVE—TVRTLE-DOVE) were identified in both the time and frequency domains. Homogeneous dephasing, inhomogeneous dephasing, intermodal frequency correlations, arithmetic signs of transition moments, and amplitude level interference between processes were all identified as causes of IRFWM lineshape variations. The signature effects of each were identified and limitations to lineshape analysis were discussed.; Semiquantitative lineshape analysis was applied to experimental DOVE-IR studies of the hydrogen bonding characteristics of acetonitrile/deuterium oxide mixtures. Simulation fits to the experimental data indicate that the inhomogeneous:homogeneous broadening ratio of the C≡N stretching and (C≡N stretching + C-C stretching) modes of hydrogen bonded acetonitrile lies between 2 and 3.5; the same ratio for free acetonitrile was assumed to be zero. Furthermore, it appears that homogeneous broadening of acetonitrile decreases upon hydrogen bond formation. A brief qualitative model is proposed to explain the observed decrease.