Direct potential fitting analysis for the A3Π1←X1Σ+ system of IBr

Doppler-limited vibrational absorption spectra of the A $\leftarrow$ X electronic transition of I${}^{79/81}$Br are measured in the 0.695 – $0.735\mu m$ and the 0.90 – $0.94\mu m$ region using a Ti:sapphire ring laser. The absorption lines belonging to $v^{\prime }\leftarrow v^{\prime \prime }={(19-32)}^{\prime }$ $\leftarrow$ (0,1)${}^{\prime \prime }$ and ${(2,3,4)}^{\prime }$ $\leftarrow$ (6,7)${}^{\prime \prime }$ for I${}^{79/81}$Br are assigned, and the center position of the $Q$ branch line belonging to over $v^{\prime }$=21, which is split into a doublet by the electric quadrupole coupling effect, was estimated. The potential models and function parameters for the $A^3{\Pi }_1$ and $X^1{\Sigma }^{+}$ states in I${}^{79/81}$Br were determined using direct potential fitting.