Knowledge Bank

High-resolution spectroscopy in the near infrared region is very important for frequency standards. We have measured the Doppler limited vibrational-rotational spectrum of ICl,, 43 (2009).} IBr,, 132 (2002).} I$2$, 271 (1997).} and Br$2$ by using a titanium sapphire laser, and have reported their spectroscopic constants. The present work presents revised spectroscopic constants for the $X$-state of Br$2$ which are obtained by performing a combined-isotopologue least-squares fit to all available data for the three isotopic species. We are also attempting to observe the lowest vibrational levels of the $A$-state in order to allow us to determine the potential energy function of this state. Measurements were made at room temperature in the region $13000-13700 cm-1$ and at 150-250C in the region $11600-13000 cm-1$. Details of these results will be presented.