A level-crossing model for infrared pump-probe spectroscopy of water

摘要

The level-crossing model is applied to pump-probe spectroscopy of the intramolecular vibration of hydrogen-bonded HDO molecules dissolved in H2O. The parameters of the model are extracted from experimental data. It is shown that within the linear approximation for the dependence of the vibrational transition frequency on the hydrogen-bridge length, the pumping light saturates not only the upsilon = 0 --> upsilon = 1, but also the upsilon = 1 --> upsilon = 2 transition, resulting in the suppression of superabsorption in transmission spectra. The non-linearity of the transition frequency may be introduced through either anharmonic corrections to the vibrational energy levels, or different curvatures of parabolic levels. As the result, the 1 --> 2 transition shifts out of resonance with the pumping field, no population of the upsilon = 2 level appears, and the transmission spectra fit better to experimental observations. [References: 14]