Knowledge Bank

Recently Hougen, Bunker and $Johns1$ derived an expression for the rovibrational Hamiltonian of a triatomic molecule allowing for a large amplitude bending vibration. We have used this Hamiltonian to compute the rovibrational energy levels of HCN in its first excited electronic state, in which it is bent. In order to have high precision experimental energy levels, several bands of the A--X system of HCN (1900 {\AA} to 1700 {\AA}) have been obtained under greater dispersion than previously used by Herzberg and $Innes.7$ Experimental and computational results will be discussed.