Spectral diagnostics of the dynamics of homo-conjugated complex [HCN.H.NCH]$^{+}$ formation

A quantum-mechanical analysis of the manifestations of the NHN hydrogen bond in the vibrational spectra of the [HCN.H.NCH]$^{+}$ linear complex along the proton transfer reaction profile is given, and the laws governing the diagnostic parameters – potential descriptors of the dynamics of this process – are established. The surface of the potential energy and harmonic frequencies of normal vibrations along the profile of the proton transfer reaction path in the system studied are calculated. It has been shown that when the [HCN.H.NCH]$^{+}$ and NCH fragments come closer together, a noticeable distortion of the forms of their skeletal vibrations occurs, up to complete mixing into the symmetric and antisymmetric forms. The frequency of the longitudinal vibration of the central proton $\nu$ (NH) varies along the reaction path from $\sim$3600 to $\sim$500 cm$^{-1}$. In the region of intersection of the terms $\nu$ (NH) and $\nu$ (CN) an abrupt nature of frequency change is detected.