Photofragment translational spectroscopy of IBr at 304 nm: Polarization dependence and dissociation dynamics

Abstract

The photodissociation dynamics of IBr has been studied at 304 nm by state-selective photofragment translational spectroscopy. Velocity distributions, anisotropy parameters, and relative quantum yields are obtained for the ground I(2P3/2) and spin–orbit excited state I*(2P1/2) iodine atoms, which are produced from photodissociation of IBr at this wavelength. Two sharp velocity distributions observed for the I channel suggest the two dissociation pathways that correlate with ground-state iodine formation. Based on the expected translational energy release and the energy separation between the peaks, the two distributions have been assigned to dissociation of IBr to form I(2P3/2)+Br(2P3/2) and I(2P3/2)+Br*(2P1/2) with the former channel appearing at higher translational energy. The I* distribution shows one strong peak indicating that there is one dominant channel for formation of I* atoms at this wavelength which has been assigned to dissociation of IBr to form I*(2P1/2)+Br(2P3/2) with a quantum yield of 0.1. The I* signal formed from the I*(2P1/2)+Br*(2P1/2) dissociation channel is observed very weakly. The observed anisotropy parameter indicates that the I+Br* product (β=−0.7) is formed mainly from the perpendicular 1Π1(2341)←X transition while the I*+Br channel (β=1.8) is formed predominantly from the parallel 3Π0+(2341)←X transition followed by curve crossing to the 3Σ0+−(2422) state. The recoil energy dependence of the anisotropy parameter in the I atom produced in the I+Br channel shows a positive β value above maximum of the peak recoil energy and a negative value below the peak maximum of the recoil energy distribution. These results are interpreted in terms of the presence of more than one path for the formation of I+Br photoproduct with opposite polarization for their absorbing transitions, most likely the 3Π0+(2341)←X and the 3Π1(2341)←X transitions. The possible excited state dynamics which give the observed results are discussed in terms of the previously proposed potential energy diagrams for IBr and ICl.

Nonadiabatic wave packet dynamics: Experiment and theory in IBr

“…20 Subsequent tunable and ultraviolet ͑UV͒ laser studies expanded on these results and added details on the potentials. [21][22][23][24] In Fig. 1 both diabatic ͑dashed lines͒ and adiabatic ͑solid lines͒ potential energy curves are shown for the IBr molecule.…”

Quantum Interference Effects Theoretically Found in the Photodissociation Processes of the Second Absorption Bands of ICl and IBr Molecules

“…The experimental spectroscopy in the first absorption band of IBr has also been extensively studied, 4,11-14 and the predissociation process has been theoretically studied thoroughly. 1,[15][16][17][18][19][20][21][22] Photodissociation from their second absorption bands in the ultraviolet region has also been studied extensively, and the branching ratios and anisotropy parameters of the 4 photofragments have been reported for ICl 10,[23][24][25][26] and IBr [27][28][29] . The following dissociation channels are energetically possible by the excitations in their second absorption bands, IX + hν → I + X, → I + X * , → I * + X,…”

Continuum state spectroscopy: A high resolution ion imaging study of IBr photolysis in the wavelength range 440–685 nm

“…26 For completeness, we note that the literature also contains reports of at least three PTS studies of IBr photolysis at shorter wavelengths ͑spanning the range 248-308 nm͒. [27][28][29] Ion imaging methods 30,31 and, particularly, the more recent velocity mapping variant of the technique, 32 are now widely recognized as providing a particularly direct and informative visualization of product branching ratios and the velocity ͑speed and angular͒ distribution of fragments arising in photofragmentation processes. Here, as part of an ongoing program devoted to the ''continuum state spectroscopy'' of halogens and interhalogens, 10,33,34 we report the use of such methods in a comprehensive study of the photolysis of jet-cooled IBr molecules over the wavelength range 440-685 nm.…”