Experimental and theoretical investigations of the He⋯I2 rovibronic spectra in the I2 B–X, 20–0 region

Abstract

The laser-induced fluorescence and action spectra of I2 in a helium supersonic expansion have been recorded in the I2 B-X, 20-0 region. Two features are identified within the spectra. The lower-energy feature arises from transitions between states that are localized in a T-shaped conformation on both the X- and B-state potentials. The higher-energy feature reflects transitions from states that are localized in a linear conformation on the X state to states that have energies that are larger than the barrier for free rotation of the rare gas atom about the I2 molecule on the B-state potential. Ground-state binding energies of 16.6(6) and 16.3(6) cm-1 were determined for the T-shaped and linear conformers, respectively. These spectra are compared to those calculated using the experimentally determined rotational temperatures. Based on the agreement between the experimental and calculated spectra, the binding energies of the J'=0 states with 0 and 2-6 quanta of excitation in the He...I2 bending mode on the B state were determined. Several models for the B-state potential were used to investigate the origins of the shape of the contour of the higher-energy feature in the spectra for He...I2 and He...Br2. The shape of the contours was found to be relatively insensitive to the choice of potential. This leads us to believe that the spectra of these systems are relatively insensitive to the parameters of the B-state potential energy surface and are more sensitive to properties of the halogen molecule.

Ab initio vibrational predissociation dynamics of He–I2(B) complex

“…The first feature shifted nearly 4 cm −1 to higher energies in the experiments by Ray et al 12 can be attributed to the transition between the initial T-shaped state of HeI 2 ͑X , v =0͒ and the excited complex HeI 2 ͑B , vЈ , nЈ =0͒ in its ground vdW state. The computed blueshifts based on T-shaped binding energies are reported in Table III Blueshifts were also measured for the first excited band, which corresponds to the C band in the early work of Smalley et al 3 This band has been attributed 3,12 to the contribution of vdW excited modes nЈ ജ 2 for the B state. In order to analyze their recent experimental data, Ray et al 12 have relied on a semiempirical pairwise-additive B-state potential that also displays a single well about the T-shaped configuration.…”

“…4,5 In addition, Jahn et al have reevaluated the groundstate binding energy of the HeI 2 molecule based on their experimental results on HeBr 2 . 11 Recently, Ray et al 12 have published a joint theoretical-experimental study of the B ← X spectrum, which they interpret as resulting from the contribution of multiple ͑T-shaped and linear͒ conformers of He-I 2 complex. Furthermore, they have reported new estimates of the binding energies and structures of the ground and B excited state isomers.…”

Full-dimensional multi configuration time dependent Hartree calculations of the ground and vibrationally excited states of He2,3Br2 clusters

“…The first experiments on van der Waals (vdW) clusters consisting of a dihalogen molecule and rare-gas atoms have been performed by Levy et al, 1,2 followed by a large number of studies on systems such as He n I 2 (n=1-3), 3,4 Ne n I 2 (n=1-6), 2,5,6 Ne n Br 2 , 7 Rg 1,2 X 2 (Rg=He, Ne, Ar and X=Cl, Br), [8][9][10][11] Ne n ICl (n=1-5), 12,13 He n ICl ((n=1-3). 14,15 More recently the interest in studying such species has been intensified due to additional experiments, rotational, and infrared spectroscopy on doped helium nanodroplets, [16][17][18] and on small/intermediate-sized doped helium clusters.…”

Laser-Induced Rotation of Iodine Molecules in Helium Nanodroplets: Revivals and Breaking Free

“…However, classically, a high-fluence pulse can induce such a fast rotation of the He-dressed molecule that helium atoms detach due to the centrifugal force -a mechanism which, we believe, is responsible for the sharp structure appearing in the prompt alignment peak. A simple criterion for detaching one He atom is: E rot (He) > E binding (He), where E rot (He) = [20,26]. Table I displays E rot (He) calculated for the different fluences.…”