Knowledge Bank

The electronic spectrum of HF has been studied in emission and in absorption. In 1959 Johns and $Barrow1$ analyzed the $V1\Sigma -X1\Sigma$ at low resolution in the region 2650-2050 {\AA}. This spectrum has been rephotographed at higher resolution and the observation has been extended down to 1480 {\AA}. About 60 bands have been identified. The relative position of the ground and upper state vibrational levels has been determined from $v^\{\backslash prime\}^\{\backslash prime\}\; =\; 7$ to $v^\{\backslash prime\}^\{\backslash prime\}\; =\; 19$ and from $v\prime =0$ to $v\prime =10$. Since the vibrational energies up to $v^\{\backslash prime\}^\{\backslash prime\}\; =\; 9$ have been determined from infrared measurements by Mann et $al.2$, the absolute energies of all the newly measured levels have been determined. From them a new RKR potential has been obtained together with a dissociation energy value $D0(HF)=47333\pm 60$ $cm-1$ $(5.8684\pm 007eV)$ which agrees with the previous value given by Johns and Barrow within their estimated error. The absorption spectrum of HF has been photographed in the third and fourth orders of a 10-m spectrograph. A complex spectrum of many discrete rotational lines has been observed from 1040 {\AA} to the ionization limit and even beyond these are bands showing rotational structure. The analysis shows that 45 bands (from 14-0 to 63-0) belong to the $V1\Sigma -X1\Sigma$ transition. Many of the higher observed bands are perturbed with interaction with Rydberg states. A strong $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi -X1\Sigma$ system with $T0\simeq 105 090.8$ $cm-1$, $\Delta G\prime (12)\simeq 2636$ $cm-1$ and $B\prime \simeq 16.0$ $cm-1$ has been observed together with a slightly lower energy $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi -X1\Sigma$ system. We interpreted these as arriving from a $3p\sigma$ Rydberg orbital and associate the $3s\sigma$ orbital with a continuous absorption which has been observed at longer wavelengths.