Knowledge Bank

We report the observation the second overtone $band1$ $(3\nu 2(1=1)\leftarrow 0)$ of $H3+$ using a 1.45 $\mu m$ InGaAsP near infrared diode laser with the short external cavity mode control technique developed at McMaster $University.2$ $H3+$ was generated using 1.5 Torr of $H2$ with or without $4\sim 5$ Torr of He in a liquid-$N2$ cooled multiple-inlet-multiple-outlet discharge cell. The $H3+$ signal was detected with velocity modulation or ion concentration modulation in an AC glow discharge. Altogether four lines have been observed in the region of 6860--6925 $cm-1$. The positions of the lines were determined using a wavemeter calibrated with $H2O$ reference lines. The assignment of the transitions is based on Miller and Tennyson’s first principles $calculation3$ and on observed temperature dependence of the relative intensities. Extended search of other transitions is being conducted. It is our hope that this observation may lead to detection of $H3+$ in higher vibrational states in Jupiter and other astronomical objects, and that it may also help in the assignment of the laboratory FTIR emission spectrum of hydrogen plasma.