G2 Molecular Orbital Study of the Reactions of Water with Cl⁺(³P) and Cl⁺(¹D)

Abstract

G2 ab initio molecular orbital calculations have been carried out to study the potential energy surfaces (PESs) associated with the reactions of Cl + in its 3 P ground state and in its 1 D first excited state with water. Similar to what was found for the reactions involving F + , the [H 2 ,Cl,O] + triplet state cations are weakly bound species, while the corresponding singlets are covalently bound species. As a consequence, although the PES of Cl + -( 3 P) lies 33.0 kcal/mol below that of the Cl + ( 1 D), the global minimum of the singlet potential energy surface lies 34.0 kcal/mol below the global triplet minimum. We have also found significant differences between the [H 2 ,Cl,O] + species and their fluorine-containing homologs regarding both their bonding and relative stabilities. These differences are more pronounced in the case of the triplets where the relative stabilities of the [H 2 ,F,O] + minima are completely reversed when fluorine is replaced by chlorine. As a result, most of the products of the reactions of F + with water cannot be formed in Cl + + H 2 O reactions, although also in this case the most likely process is the single charge transfer, in agreement with the experimental evidence. However, the formation of OH + becomes exothermic when Cl + reacts in its 1 D excited state. The estimated heat of formation for the most stable H 2 OCl + singlet state species is 193 ( 2 kcal/mol.

Mechanism of the Hydrolysis of Halogen Nitrates in Small Water Clusters Studied by Electronic Structure Methods

“…[36][37][38][39][40][41][42] Ab initio calculations predict both the H 2 OCl + 42 and H 2 OBr + 54 ions to be stable in small water clusters where the most stable isomer involves protonation of oxygen. 55,90,91 However, quantum chemical calculations 45 of the ClONO 2 hydrolysis pathway do not involve the H 2 OCl + intermediate, and recent calculations and analysis of the available spectroscopic data argue against the formation of H 2 -OCl + . 86 Identification of H 2 OBr + in RAIRS experiments is made primarily on the assignment of the distinct H 2 O deformation mode measured at 1650 cm -1 .…”

“…Bell and Gelles have observed H 2 OX + (X = Cl, Br, and I), whereas Eigen and Kustin appear to rule out the formation of such species in aqueous solution studies of X 2 + H 2 O → XOH + H + + X - . More recently, Ramondo and Sodeau report reaction pathways involving the H 2 OBr + ·(H 2 O) n ·Br - ion pair in RAIRS studies of Br 2 hydrolysis, which are competitive with routes occurring via an H 3 O + ion, while the hypochlorous ion (H 2 OCl + ) is implicated in the hydrolysis of ClONO 2 . − Ab initio calculations predict both the H 2 OCl + 42 and H 2 OBr + 54 ions to be stable in small water clusters where the most stable isomer involves protonation of oxygen. ,, However, quantum chemical calculations 45 of the ClONO 2 hydrolysis pathway do not involve the H 2 OCl + intermediate, and recent calculations and analysis of the available spectroscopic data argue against the formation of H 2 OCl + …”

Reactions of F+(3P) and F+(1D) with Silicon Oxide. Possibility of Spin-Forbidden Processes

“…[4][5][6][7] In this respect the role of high-level ab initio molecular orbital techniques [8][9][10][11][12][13] was of great importance in elucidating these mechanisms. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] Actually, in many occasions, the ab initio or density functional theory calculations are the only alternative available to investigate the structures of ionic species, which, very often, are elusive to experimental observation. Besides, high-level theoretical methods reach the so-called chemical accuracy, and therefore, many thermodynamic properties of neutral and charged species can be estimated within (2.0 kcal/mol of the experimental values, when available.…”

“…Gas-phase ion processes are of great relevance in atmospheric and interstellar chemistry. − It is nowadays well established that ion−molecule reactions seem to be in the origin of the different species detected inside interstellar clouds. , However, in general, the only information available in most of these processes is the product distribution, but very little is known about the mechanism leading to these products. − In this respect the role of high-level ab initio molecular orbital techniques − was of great importance in elucidating these mechanisms. − Actually, in many occasions, the ab initio or density functional theory calculations are the only alternative available to investigate the structures of ionic species, which, very often, are elusive to experimental observation. Besides, high-level theoretical methods reach the so-called chemical accuracy , and therefore, many thermodynamic properties of neutral and charged species can be estimated within ±2.0 kcal/mol of the experimental values, when available. − High accuracy is important in this field because in interstellar space only exothermic processes are likely to occur, due to the extreme interstellar conditions of low temperature and density, and therefore an accurate knowledge of the topology of the corresponding potential energy surface (PES) is of critical importance.…”

Theoretical Survey of the Potential Energy Surfaces Associated with the N+(3P,D) + C2H4Reactions in the Gas Phase

“…This is the case of the halogen cations and N + where the first excited 1 D state is relatively close in energy to the ground 3 P state. 22 Quite importantly, however, when the ion is attached to a neutral molecule, a reverse stability order is often found and singlets become lower in energy than triplets, 8,13,[23][24][25][26][27][28] reflecting the stronger bonds between the ion and the neutral in the former. Accordingly, different crossovers between singlet and triplet PESs can be envisaged, 13,26,28 and therefore in many of these processes spin-forbidden reaction mechanisms play an important role, as has been suggested before for N + + SH 2 and N + + H 2 CO reactions.…”