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

We have investigated the ultraviolet photodissociation of IBr using core-sa mpled state-selective ion time-of-flight mass spectrometry on the iodine an d bromine atom products. The branching ratios and anisotropy parameters wer e determined for the I(P-2(3/2)) + Br(P-2(3/2)), I(P-2(3/2)) + Br(P-2(1/2)) , and I(P-2(1/2)) + Br(P-2(3/2)) channels at 248, 267, and 304 nm. We find no evidence for the I(P-2(1/2)) + Br(P-2(1/2)) channel at any wavelength. T he results provide information on the relative transition probabilities for the (3)Pi(1)(2341), (3)Pi(0+)(2341), and (1)Pi(1)(2341) excited states in the absorption band centered at 270 nm. We have further evaluated the nonad iabatic curve crossing probability for the avoided crossing between the (3) Pi(0+)(2341) and (3)Sigma(0+)(-)(2422) states over a range of wavelengths f rom 250 to 270 nm. The wavelength-dependent curve crossing probability for the avoided crossing is modeled using one-dimensional Landau-Zener theory i n 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 analo gous interhalogen molecules is also provided. (C) 1999 Elsevier Science B.V . All rights reserved.