Knowledge Bank

The binary complex between HF and HC1 at $\nu HF=3$ level, which has two stable forms: HF-HC1 and HC1-HF, is studied recently by molecular beam laser induced fluorescence with an intracavity Ti-sapphire ring $lasera$ and the detection of HF $\Delta \nu =2\leftarrow 0$ emission. Similar to previously reported $K=0-0(300000)\leftarrow (000000)$ transition of $HF-HC1b$, the $K=1-0$ subband seen at $11353.2cm-1$ shows significant rotational dependence to the predissociation linewidths, varying from 1.3 to 2.4 GHz. The rotational A constant of $43.5cm-1$ clearly indicates that the vibration-averaged angle between the HF axis and a-axis decreases over valence excitation, compared to $40.1cm-1$ at $\nu HF=1$ level. Another weaker Q-branch band observed at $11351.7cm-1$, with slightly narrower linewidths and little apparent J dependence, is tentatively assigned to the $K=1-0(301000)\leftarrow (000000)$ combination transition of HC1-HF. The 2D vibration-averaged ab initio interaction potential of the complex predicts the HC1-HF form becomes more stable than HF-HC1 through the valence excitation. The isotopic $variationc$ of predissociation lifetime for the observed transitions is still under investigation.