dorsal/arxiv
View SchemaAmmoniated electron as a solvent stabilized multimer radical anion
| Authors | I. A. Shkrob |
|---|---|
| Categories | |
| ArXiv ID | physics/0509137 |
| URL | https://arxiv.org/abs/physics/0509137 |
| DOI | 10.1021/jp055500z |
Abstract
The excess electron in liquid ammonia ("ammoniated electron") is commonly viewed as a cavity electron in which the s-type wave function fills the interstitial void between 6-9 ammonia molecules. Here we examine an alternative model in which the ammoniated electron is regarded as a solvent stabilized multimer radical anion, as was originally suggested by Symons [Chem. Soc. Rev. 1976, 5, 337]. In this model, most of the excess electron density resides in the frontier orbitals of N atoms in the ammonia molecules forming the solvation cavity; a fraction of this spin density is transferred to the molecules in the second solvation shell. The cavity is formed due to the repulsion between negatively charged solvent molecules. Using density functional theory calculations for small ammonia cluster anions in the gas phase, it is demonstrated that such core anions would semi-quantitatively account for the observed pattern of Knight shifts for 1-H and 14-N nuclei observed by NMR spectroscopy and the downshifted stretching and bending modes observed by infrared spectroscopy. It is speculated that the excess electrons in other aprotic solvents (but not in water and alcohols) might be, in this respect, analogous to the ammoniated electron, with substantial transfer of the spin density into the frontier N and C orbitals of methyl, amino, and amide groups forming the solvation cavity.
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"abstract": "The excess electron in liquid ammonia (\"ammoniated electron\") is commonly\nviewed as a cavity electron in which the s-type wave function fills the\ninterstitial void between 6-9 ammonia molecules. Here we examine an alternative\nmodel in which the ammoniated electron is regarded as a solvent stabilized\nmultimer radical anion, as was originally suggested by Symons [Chem. Soc. Rev.\n1976, 5, 337]. In this model, most of the excess electron density resides in\nthe frontier orbitals of N atoms in the ammonia molecules forming the solvation\ncavity; a fraction of this spin density is transferred to the molecules in the\nsecond solvation shell. The cavity is formed due to the repulsion between\nnegatively charged solvent molecules. Using density functional theory\ncalculations for small ammonia cluster anions in the gas phase, it is\ndemonstrated that such core anions would semi-quantitatively account for the\nobserved pattern of Knight shifts for 1-H and 14-N nuclei observed by NMR\nspectroscopy and the downshifted stretching and bending modes observed by\ninfrared spectroscopy. It is speculated that the excess electrons in other\naprotic solvents (but not in water and alcohols) might be, in this respect,\nanalogous to the ammoniated electron, with substantial transfer of the spin\ndensity into the frontier N and C orbitals of methyl, amino, and amide groups\nforming the solvation cavity.",
"arxiv_id": "physics/0509137",
"authors": [
"I. A. Shkrob"
],
"categories": [
"physics.chem-ph"
],
"doi": "10.1021/jp055500z",
"title": "Ammoniated electron as a solvent stabilized multimer radical anion",
"url": "https://arxiv.org/abs/physics/0509137"
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