Knowledge Bank

Due to the large anharmonicity and vibration-rotation interactions in the $H3+,$ the IR forbidden transitions $v1+v2\leftarrow v2$ and $v1\leftarrow$ 0 can borrow intensity from the allowed $2v2(1=2)\leftarrow v2$ and $v2\leftarrow 0$ bands. Using the ab initio $calculation1$ as a guide, we searched for these transitions using the difference frequency laser system in the region from 2840 $cm-1$ to 3280 $cm-1$. $H3+$ was produced in a liquid nitrogen cooled AC glow discharge of $H2$ and He mixtures. About 170 new lines have been observed, and the analysis is under way. Up to now, 12 lines have been assigned to the band $v1+v2\leftarrow v2$; and 2 lines to $ v_{1}\leftarrow 0$. During this process, we have also assigned many new transitions for the other bands. The forbidden transitions of $H3+$ is of special interest for astrophysics since it is an important mechanism to cool down the excited $H3+$ in the space. It also gives absolute rovibrational energy values for the $ v_{1}$ and the $ v_{1} + v_{2}$ states.