Frequency optimized potential energy functions for the ground-state surfaces of HCN and HCP

Potential energy functions for the ground states of the linear triatomics HCN, HNC ($\text{X}\text{?}{}^1\text{Σ}{}^{\mathrm{+}}$) and HCP ($\text{X}\text{?}{}^1\text{Σ}{}^{\mathrm{+}}$) were derived, by minimizing the difference between the observed vibrational frequencies and those calculated from the potentials by a variational method. Good agreement is obtained between the observed and calculated spectra for HCN and HNC. For the HCP system, a secondary minimum is predicted to lie on the ground-state surface (linear HPC) having dimensions $\text{R}{}_{\mathrm{<mtext>HP</mtext>}}\text{= 1.43}\text{A}\text{?}$, $\text{R}{}_{\mathrm{<mtext>CP</mtext>}}\text{= 1.56}\text{A}\text{?}$, and an energy of 3.8 eV above the HCP ($\text{X}\text{?}{}^1\text{Σ}{}^{\mathrm{+}}$) minimum.