Predicting PH vibrations of gas phase molecules and surface-adsorbed species using bond length-frequency correlations

The high frequency XH (e.g., X = C, Si) stretching modes in small molecules are only slightly perturbed by other vibrational modes present in the system. The isolated frequencies, in these cases, exhibit a linear relationship with the corresponding bond lengths. Here, we study such a bond length-frequency correlation in the case of PH stretching vibrations for molecules in the gas phase as well as for surface-adsorbed species. Although a high degree of linear correlation is found, there is a small dependence on the local coordination around P, leading to significant deviations in some cases. By a careful analysis, we show that such correlations can be used to predict new surface frequencies without computing the Hessian matrix explicitly.