Knowledge Bank

The $He2$ molecule is known to have many electronic transitions between Rydberg states in visible and ultraviolet regions. However, in infrared region only two bands $b3\Pi g-a3\Sigma u+$ and $B1\Pi g-A1\Sigma u+$ have been studied by using a DC discharge method so far. Recently we developed a time resolved Fourier transform spectroscopy with high resolution Bruker IFS 120 HR by using micro controller $SXa$. In the present study, the FT system was applied to infrared emission spectroscopy of $He2$ which was produced by a pulsed discharge in He with pulse width of $20\mu$sec and 1 A peak-to-peak current. In the $1800-10000cm-1$ region, many electronic transitions have been observed in addition to the previously reported two bands. From observed time profiles of emission spectra, Rydberg states with higher energy than the b state are produced efficiently in afterglow plasma after termination of the discharge. A least-squares analysis was carried out for the $h3\Sigma u+-g3\Sigma g+$ and $g3\Sigma g+-d3\Sigma u+$ bands in the $3200cm-1$ region to determine the molecular constants. A transition from an un-identified state to the $d3\Sigma u+$ state has been observed with irregular P- and R- branch intensities.