Short-range and long-range solvent effects on charge-transfer-to-solvent transitions of I− and K+I− contact ion pair dissolved in supercritical ammonia

Abstract

Articles you may be interested inVertical excitation and electron detachment energies associated with the optical absorption of iodide ions dissolved in supercritical ammonia at 420 K have been calculated in two limiting scenarios: as a solvated free I − ion and forming a K + I − contact ion pair ͑CIP͒. The evolution of the transition energies as a result of the gradual building up of the solvation structure was studied for each absorbing species as the solvent's density increased, i.e., changing the NH 3 supercritical thermodynamic state. In both cases, if the solvent density is sufficiently high, photon absorption produces a spatially extended electron charge beyond the volume occupied by the solvated solute core; this excited state resembles a typical charge-transfer-to-solvent ͑CTTS͒ state. A combination of classical molecular dynamics simulations followed by quantum mechanical calculations for the ground, first-excited, and electron-detached electronic states have been carried out for the system consisting of one donor species ͑free I − ion or K + I − CIP͒ surrounded by ammonia molecules. Vertical excitation and electron detachment energies were obtained by averaging 100 randomly chosen microconfigurations along the molecular dynamics trajectory computed for each thermodynamic condition ͑fluid density͒. Short-and long-range contributions of the solventϪdonor interaction upon the CTTS states of I − and K + I − were identified by performing additional electronic structure calculations where only the solvent interaction due to the first neighbor molecules was taken into account. These computations, together with previous experimental evidence that we collected for the system, have been used to analyze the solvent effects on the CTTS transition. In this paper we have established the following: ͑i͒ the CTTS electron of free I − ion or K + I − CIP presents similar features, and it gradually localizes in close proximity of the iodine parent atom when the ammonia density is increased; ͑ii͒ for the free I − ion, the short-range solvent interaction contributes to the stabilization of the ground state more than it does for the CTTS excited state, which is evidenced experimentally as a blueshift in the maximum absorption of the CTTS transition when the density is increased; ͑iii͒ this effect is less noticeable for the K + I − ion pair, because in this case a tight solvation structure, formed by four NH 3 molecules wedged between the ions, appears at very low density and is very little affected by changes in the density; ͑iv͒ the long-range contribution to the solvent stabilization can be neglected for the K + I − CIP, since the main features of its electronic transition can be explained on the basis of the vicinity of the cation; ͑v͒ however, the long-range solvent field contribution is essential for the free I − ion to become an efficient CTTS donor upon photoexcitation, and this establishes a difference in the CTTS behavior of I − in bulk and in clusters.

Microsolvation of sodium acetate in water: Anion photoelectron spectroscopy and ab initio calculations

“…Dissolved salts play important roles in chemical reactions, 1,2 biochemistry, 3,4 marine chemistry, 5 atmospheric chemistry, 6 and our daily life. 7 Therefore, many theoretical [8][9][10][11][12][13][14][15][16][17][18][19] and experimental [20][21][22][23][24][25][26][27][28][29] studies have investigated the microscopic mechanisms of salt dissolution. Special attention has been paid to investigate the transition between salt contact ion pairs (CIPs) and solvent-separated ion pairs (SSIPs) in water, 13,30 as well as the correlation of salt effects with the Hofmeister series.…”

First principles multielectron mixed quantum/classical simulations in the condensed phase. II. The charge-transfer-to-solvent states of sodium anions in liquid tetrahydrofuran

“…45 This distinguishes our approach from quantum mechanics/molecular mechanics ͑QM/MM͒ methods that perform electronic structure calculations on solute-solvent configurations generated with approximate interactions from purely classical simulations. 43,52,53 The rest of the paper is organized as follows. In Sec.…”

Comparison of the Microsolvation of CaX2 (X = F, Cl, Br, I) in Water: Size-Selected Anion Photoelectron Spectroscopy and Theoretical Calculations

“…Understanding the solvation of salts in water is very important in the fields of physical chemistry, biochemistry, marine chemistry, and atmospheric chemistry. − The interactions between salt ions and water molecules have nonnegligible effects on water hydrogen-bond networks, the solubility of different substances, and chemical reactions in aqueous solutions. − Many experimental − and theoretical studies − have been performed to investigate the solvation processes of salts in water at the molecular level. To provide detailed information about the transition between salt contact ion pairs (CIPs) and solvent-separated ion pairs (SSIPs) with an increasing number of water molecules, in the last ten years, we investigated the structures and properties of a series of salt-water clusters using the technique of size-selected anion photoelectron spectroscopy combining with theoretical calculations. − …”

“…In addition to the studies in the condensed phases, many studies were conducted in the gas phase. The structures of Ca 2+ (H 2 O) − clusters were explored using infrared multiple photodissociation action spectroscopy (IRMPD) . The coordination numbers of Ca 2+ in Ca 2+ (H 2 O) n clusters were studied using threshold collision-induced dissociation (CID) and blackbody infrared radiative dissociation (BIRD) experiments combined with theoretical calculations. , Many theoretical studies have also been conducted to investigate the solvation of Ca 2+ in water. − The geometric and electronic structures of calcium water complexes with one and two solvation shells were studied by means of high-level quantum calculations .…”