Knowledge Bank

The long, irregular vibrational structure of the $B¯(2\Pi i)$ state of $N2O+$ is interpreted as a progression of Fermi resonances between pairs of vibrational subbands of the $B¯$ state that correspond to $2\nu 2+(v-1)\nu 3$ and $v\nu 3$. Because of anharmonicity in the $\nu 3$ progression, the separations between successive pairs of interacting bands vary throughout the progression, resulting in variable magnitude Fermi interactions. This model, rather than the more usual one that incorporates overtones of $\nu 2$ is shown to accurately describe the experimental data.