Photodissociation of gas-phase carbon dioxide ion-molecule cluster ((CO2)2+) in the visible wavelength range: observation of two photodissociation processes

Abstract

The results of a study of the photodissociation of the carbon dioxide ion-molecule cluster, (C02)2+, from 458 to 650 nm are presented. The experiments were performed with a high-energy ion beam crossed with a laser beam. C02+ was the only product observed. Photodissociation kinetic energy release distributions and angular distributions were measured. The kinetic energy release distributions are bimodal indicating that C02+ is generated by two mechanisms. The product peak shapes were simulated by the measured product velocity distributions and two product angular distributions of the form 1 + ß 2(cos ) with ß = 1.0 for the high-energy component in the kinetic energy release distribution and ß = 0.25 for the low-energy component. The results suggest that the mechanisms leading to C02+ are rapid fragmentation on a repulsive surface on a time scale which is short compared to a rotational period and statistical vibrational predissociation (statistical unimolecular dissociation) of highly vibrationally excited ground electronic state (C02)2+ on a time scale which may be longer than a rotational period. Phase space calculations of the statistical vibrational predissociation component compare well with our results. The analysis suggests that 11% of the C02+ product is formed by statistical vibrational predissociation at 650 nm and 22% at 458 nm; the remainder is formed by direct dissociation from a repulsive surface. The average product relative kinetic energy increases with increasing photon energy and varies in a linear fashion with the available energy.

IR photodissociation spectroscopy of (OCS)n+ and (OCS)n− cluster ions: Similarity and dissimilarity in the structure of CO2, OCS, and CS2 cluster ions

“…For homo-dimer radical ions, it is often seen that the intermolecular charge resonance interaction occurs in them, giving a symmetrical species; the charge is equally shared by the two components. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] The dimer ion form is kept as a dimer ion core in some homo-molecular cluster ions, such as (benzene) n + . 13,14 However, the charge distribution of cluster ions is not predictable so easily on the basis of IE, PA, or EA.…”

An IR study of (CO2)n+ (n=3–8) cluster ions in the 1000–3800 cm–1 region

“…Investigation of ͑CO 2 ͒ n + includes mass spectroscopy with photoionization and electron-impact ionization, 1-13 photodissociation ͑PD͒ spectroscopy, [14][15][16][17][18][19] infrared ͑IR͒ and visible absorption spectroscopy in the gas phase, matrices, and supercritical media, [20][21][22][23][24] and quantum chemical calculations. [25][26][27] Measurement of thermochemical values for the association reaction, ͑CO 2 ͒ n−1 + +CO 2 → ͑CO 2 ͒ n + , by highpressure mass spectrometry gave the binding energy of these clusters.…”

“…The dimer ion core structure of ͑CO 2 ͒ n + was confirmed with PD spectroscopy in the visible region. [14][15][16][17][18] Absorption of ͑CO 2 ͒ 2 + in the visible region is attributed to a transition between two charge resonance ͑CR͒ states. Wave functions of the CR states are given by ⌿ CR = ͑M a + ͒ · ͑M b ͒ Ϯ ͑M a ͒ · ͑M b + ͒, where ͑M + ͒ and ͑M͒ stand for wave functions of CO 2 + ͑X 2 ⌸ g ͒ and CO 2 ͑X 1 ⌺ g + ͒, respectively.…”

“…As a result of the CR interaction, the intermolecular bonding MO is formed ͑21␤͒ for isomer 2A. The CR transition observed in the visible region is due to the electron promotion from 21␤ to 22␤ [14][15][16][17][18]. Results of vibrational analysis for isomer 2A are collected inTable II.…”

Infrared spectra of the C2O4+ cation and C2O4− anion isolated in solid neon

“…The cluster cations have been formed by photoionization of neutral clusters, 1,2 their binding energies and photodissociation dynamics determined. [3][4][5] The cluster anions have been prepared by electron attachment, and their photoelectron spectra and vertical detachment energies measured. [6][7][8] The carbon dioxide neutral dimer has been extensively studied by both theory 9 and experiment, and its nonpolar C 2h configuration has been determined; 10 however, the structure and stabilities of the dimer cation and the dimer anion remain open.…”