Calculation of the vibrational spectrum of the triphosphate anion

Abstract

A large amount of experimental material on the vibrational spectra of phosphates with different degrees of condensation has now been accumulated. In the interpretation of these spectra empirical assignment of the vibrational frequencies based on symmetry considerations and an assumption regarding the characteristic nature of the vibrations of different groups of atoms is widely used. Calculations of the vibrational spectra, performed for a small number of compounds (see, e.g., [1-6], in general confirm the results of empirical assignment and hence confirms the assumption regarding the characteristic nature of a number of stretching vibrations in different phosphates. However in [7] on the basis of the calculation of the vibrational spectrum of the triphosphate anion P30~ a conclusion was reached that only some of the frequencies can be assigned to vibrations of specific groups of atoms (the terminal PO~, middle P02, and bridge POP, groups), but the majority of normal modes are mainly mixed. This, however, contradicts the results of the calculation performed for the P30~7 anion in [6]. Taking into account the existence of limitations and assumptions in [6, 7], whose effect on the interpretation of the spectra will be discussed below, we recalculated the vibrational spectrum of triphosphate anion to resolve the existing contradiction.