The ultraviolet photodissociation dynamics of IBr studied using state-selective translational spectroscopy Original Research Article

We have investigated the ultraviolet photodissociation of IBr using core-sampled state-selective ion time-of-flight mass spectrometry on the iodine and bromine atom products. The branching ratios and anisotropy parameters were determined for the I(2P3/2)+Br(2P3/2), I(2P3/2)+Br(2P1/2), and I(2P1/2)+Br(2P3/2) channels at 248, 267, and 304 nm. We find no evidence for the I(2P1/2)+Br(2P1/2) channel at any wavelength. The results provide information on the relative transition probabilities for the 3Π1(2341), 3Π0+(2341), and 1Π1(2341) excited states in the absorption band centered at 270 nm. We have further evaluated the nonadiabatic curve crossing probability for the avoided crossing between the 3Π0+(2341) and 3Σ−0+(2422) states over a range of wavelengths from 250 to 270 nm. The wavelength-dependent curve crossing probability for the avoided crossing is modeled using one-dimensional Landau–Zener theory in order to estimate the location of the avoided crossing and the splitting between adiabats. A comparison with recent work at 267 and 304 nm and analogous interhalogen molecules is also provided.