Rotational lines of hydrogen in water

In this paper we report new calculations of the shape of the Raman rotational lines of hydrogen in solution with water. The method was based on a perturbative treatment and the calculations were performed for a system at room temperature and pressure ≈14 MPa, a thermodynamic state at which both measurements and accurate non-adiabatic calculations were available. The scope of the paper is to compare our numerical findings both with the computational results obtained with the non-adiabatic method and with the measured widths of the rotational lines. We found that our results are very similar to those obtained with the non-adiabatic method. Calculations of the widths were made with different models for the hydrogen–water intermolecular potential. The comparison of the numerical evaluations with the experimental findings allows us to judge how dependable the potential models are. The same calculations were performed also at larger pressures, up to 160 MPa. It was found that the widths of the rotational lines increased by increasing the pressure whereas, at the same pressure, they decreased when the rotational quantum number of the initial state was increased. (paper)