Knowledge Bank

We have extended the earlier $work1,2$ on the infrared spectrum of $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}HeH+$, by observing the hot band $v=2\leftarrow 1$ of $HeH+$ and fundamental bands of isotopic species $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}HeH+$, $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}HeH+$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}HeD+$. A difference frequency laser system and a diode laser have been used as tunable infrared sources and the ion velocity modulation technique was used for detection. A sealed off discharge tube was used to conserve $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}He$. Six to fourteen vibration-rotation lines have been measured for each band. An analysis of the lines gave the following values for the band origins. [FIGURE] All of the molecular constants agreed remarkably well with the results of ab initio calculations. The rotational constants of the four isotopes were used to determine the isotopically independent parameters $\Delta 10,\Delta 10$, and the $Uij$. The observed variation of line intensities as a function of the $He:H2$ mixing ratio is discussed in terms of simple ion-molecule reaction kinetics.