Selective excitation of the ion pair surface in the intracluster Ca–HCl* harpoon reaction

Abstract

The excited state reaction of calcium with hydrogen chloride has been investigated in the specific conditions of a van der Waal complex formed in a supersonic jet after laser ablation of the metal. The reaction channel leading to ground state calcium chloride has been specifically studied in this work, by laser induced fluorescence. A very high vibrational distribution has been observed for CaCl with a maximum at v=30 and extending up to the energetic limit at v∼60. This high v population distribution has been modeled with the direct interaction direct repulsion model and corresponds to an immediate energy release occurring at the transition state, i.e., at the level of the ion pair ground state Ca+(2S), HCl− surface. This results from the observation of a continuous action spectrum for the formation of the high levels of CaCl after excitation of the complex in good agreement with the direct excitation of the ground state ion pair potential. It suggests that the potential energy surface promoting the ground state formation is different from the one leading principally to excited CaCl products already observed.

Quantum stereodynamics of the Li+HF(v,j) reactive collision for different initial states of the reagent

“…A method for the direct spectroscopic investigation of the transition state is the study of the photoinitiated reaction from the van der Waals complex of the reactants. [33][34][35][36][37][38][39][40] In these kinds of experiments on M ϩHX systems, the complex is promoted to an excited electronic state of the metal atom, [34][35][36][37][38][39][40] and the generated product fragments detected show a certain rotational polarization due to the relative orientation of the reactants in the van der Waals complex. Moreover, in a recent work 41 we have shown the possibility of accessing the vicinity of the transition state on the ground electronic state by infrared excitation of the complex of Li-HF, obtaining a high efficiency in forming LiF products at total energies where the collisional reaction cross section is rather low.…”

Collisional and photoinitiated reaction dynamics in the ground electronic state of Ca–HCl

“…This last contribution was added to match the experimentally estimated dissociation energy of Menéndez et al 62 The latter estimate was based on the energetics of a reactive collision experiment, in which the product recoil energy was neglected. On the basis of the present results it may be considered that the Ca-HCl van der Waals complex formed in the experiments of Soep and co-workers [17][18][19][20] is not bound, but corresponds to one or several of these long-lived resonances, which have dissociation energies up to Ϸ650 cm −1 with respect to the corresponding HCl͑͒ asymptote. The latter value of the Ca-HCl binding energy would explain the formation of Ca-HCl complexes in competition with Ca 2 dimer formation.…”

“…Such experiments were performed either with collisions [8][9][10][11][12][13][14][15][16] or by photoinitiation from the van der Waals complex in the entrance channel. [17][18][19][20] Even though in all these studies the system is electronically excited, the formation of CaCl fragments in the ground electronic state seemed to be a major reaction path. 12,20 The Ca+ HCl reaction in the ground electronic state has not been studied before, possibly because it is highly endoergic.…”

“…[17][18][19][20] Even though in all these studies the system is electronically excited, the formation of CaCl fragments in the ground electronic state seemed to be a major reaction path. 12,20 The Ca+ HCl reaction in the ground electronic state has not been studied before, possibly because it is highly endoergic. This is shown in Fig.…”

“…[8][9][10][11][12][13][14][15][16] An interesting alternative to study such nonadiabatic processes consists of exciting the system from a van der Waals complex formed in the entrance channel of the ground electronic state reaction. [17][18][19][20] The collision reaction dynamics in the ground electronic state has been investigated experimentally for several alkaliearth atoms reacting with different hydrogen halides. [21][22][23][24][25][26][27][28][29] These studies concerned the effects of the collision energy and initial vibrational excitation of HX, as well as the final rovibrational state distribution of the fragments.…”