Reaction pathway, energy barrier, and rotational state distribution for Li (2 2PJ)+H2→LiH (X 1Σ+)+H

Abstract

By using a pump-probe technique, we have observed the nascent rotational population distribution of LiH (v=0) in the Li (2 2PJ) with a H2 reaction, which is endothermic by 1680 cm−1. The LiH (v=0) distribution yields a single rotational temperature at ∼770 K, but the population in the v=1 level is not detectable. According to the potential energy surface (PES) calculations, the insertion mechanism in (near) C2v collision geometry is favored. The Li (2 2PJ)–H2 collision is initially along the 2A′ surface in the entrance channel and then diabatically couples to the ground 1A′ surface, from which the products are formed. From the temperature dependence measurement, the activation energy is evaluated to be 1280±46 cm−1, indicating that the energy required for the occurrence of the reaction is approximately the endothermicity. As Li is excited to higher states (3 2S or 3 2P), we cannot detect any LiH product. From a theoretical point of view, the 4A′ surface, correlating with the Li 3 2S state, may feasibly couple to a repulsive 3A′ surface, from which the collision complex will rapidly break apart into Li (2 2PJ) and H2. The probability for further surface hopping to the 2A′ or 1A′ surfaces is negligible, since the 3A′ and 2A′ surfaces are too far separated to allow for an efficient coupling. The Li (3 2P) state is expected to behave similarly. The observation also provides indirect evidence that the harpoon mechanism is not applicable to this system.

Coriolis Coupling Influence on the H+LiH Reaction

“…2,3,6-8 Bililign et al 9 conducted laser induced pump-probe far-wing scattering experiments to study the photochemical reaction Li + H 2  LiH + H. Chen et al 10 observed the nascent rotational population distribution of LiH in the atom Li plus diatom molecule H 2 reaction by using a pump-probe technique. The comprehensive chemistry of lithium in the post-recombination epoch is presented by Stancil et al 3 and the abundances of Li, Li + , Li  , LiH and LiH + were employed for calculation as a function of red-shift z for several cosmological models.…”

STATE-TO-STATE QUANTUM WAVE PACKET DYNAMICS OF THE LiH + H REACTION ON TWO AB INITIO POTENTIAL ENERGY SURFACES

“…The formation of LiH in different electronic states has been studied in several works (Chen et al 2001;Chen & Lin 2003;Bililign et al 2001). Chen et al (2001) measured the nascent rotational population distribution of the LiH molecule in its ground vibrational state in the Li * + H 2 reaction. It was concluded that the Li * + H 2 reaction is dominated by an insertion mechanism.…”

Rotational and vibrational state distributions of NaH in the reactions of Na(4S2,3D2,and6S2) with H2: Insertion versus harpoon-type mechanisms

“…13,14,16,29 The radiation sources contained two tunable dye lasers, which were pumped individually by a Nd:YAG laser operating at 10 Hz with a pulse duration of 5 -8 ns. The first dye laser at wavelength was used to prepare the Na atom in the 4 2 S, 3 2 D, and 6 2 S states at / 2 = 388.5, 342.8, and 274.9 nm by twophoton absorption, using the dyes LDS 765, LDS 698, and rhodamine 575, respectively.…”

“…8 In the endothermic reaction of Li͑2 2 P J ͒ with H 2 , Lin and coworkers obtained a single-peaked rotational population distribution of LiH͑v =0͒, which was dominated by a reaction with Li insertion into the H-H bond. 29,32 The Li͑3 2 S ,3 2 P͒ reactions do not lead to any detectable LiH product, thereby providing indirect evidence that the harpoon mechanism cannot be applied to the Li reaction. This consequence is also supported by Lee et al from a theoretical perspective.…”