An AB initio molecular orbital study of the ammonium radical

McMaster, Blair N.; Mrozek, Janusz; Smith, Vedene H.

doi:10.1016/0301-0104(82)85155-0

Cited by 37 publications

(5 citation statements)

References 32 publications

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“…Note that although the lowest harmonic frequency in NH 4 is above 1000 cm -1 , there is nevertheless a low energy barrier to decomposition to the more stable products NH 3 + H. This barrier was calculated by several groups, including by McMaster et al, Kassab and Evleth, and Boldyrev and Simons . In ref , for example, the barrier was shown to be 12 kcal/mol, uncorrected for zero-point energy (ZPE) differences.…”

Section: Resultsmentioning

confidence: 99%

Stability of the Rydberg Dimer (NH₄)₂

Wright

McKay

1996

J. Phys. Chem.

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In this paper we reexamine the stability of the dimer of the ammonium radical NH 4 reported recently by Boldyrev and Simons (J. Phys. Chem. 1992, 96, 8840). More flexible diffuse basis sets are introduced designed to give a better representation of the important 3s orbital on N, overlap from which leads to the weak Rydberg bond. At the MP2(full) level of calculation the energetic results, molecular geometry, and vibrational frequencies are generally in good agreement with Boldyrev and Simons, except for the very low-frequency modes. However, the essentially free rotation of the NH 4 monomer within the weak Rydberg two-electron bond requires further analysis of the dimer stability. Following a reaction coordinate toward the (strongly exothermic) ground state products 2NH 3 + H 2 shows that there is a very low barrier of about 2.0 kcal/mol, which disappears when corrected for zero-point energy differences. This will destabilize the dimer and make its observation improbable.

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Section: Resultsmentioning

confidence: 99%

Stability of the Rydberg Dimer (NH₄)₂

Wright

McKay

1996

J. Phys. Chem.

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“…Havriliak, Furlani, and King21 improved on their earlier calculations in 1984, and Cardy, Liotard, Dargelos, Marinelli, and Roche22 examined vibronic coupling effects in the 2T2(3p) state in 1988. The thermodynamic and kinetic stabilities of NH4 and its deuterated forms have been studied by McMaster et al, 23 Cardy et al, 24 Kaspar et al, 25 and by Kassab and Evleth. 26 The conclusions of these papers concerning the relative energies and stabilities of the Rydberg states are qualitatively similar.…”

Section: B Nh4-mentioning

confidence: 99%

Double-Rydberg molecular anions

Simons¹,

Gutowski²

1991

Chem. Rev.

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“…Although we have continued to search for alternative candidates (e.g., (H 3 O) 2 , H 3 ONH 4 and others 14 ) that might form stronger two-electron Rydberg-Rydberg bonds with higher barriers, we have not yet found a satisfactorily convincing candidate. However, it is important to keep in mind, as noted earlier, that the corresponding one-electron Rydberg-Rydberg bound cations are predicted to be stable with respect to dissociation and thus likely represent better candidates for experimental observation.…”

Section: Introductionmentioning

confidence: 97%

“…Nevertheless, we decided to examine whether overlap of the a 1 Rydberg-like orbitals on two neighboring NH 4 units would provide a strong enough attraction to stabilize (NH 4 ) 2 sufficiently to render it stable to fragmentation into 2 NH 4. . The energy required to effect the transition from (NH 4 ) 2 to 2 NH 4 , with the bond lengths and angles held at the respective equilibrium values for (NH 4 ) 2 and NH 4 , we define as the strength of the twoelectron Rydberg bond in this case.…”

Section: Introductionmentioning

confidence: 99%

“…Neutral NH 4 is known to be electronically and locally geometrically stable at this tetrahedral geometry but unstable (by ca. 0.7 kcal/mol [2][3][4][5][6][7] ) with respect to fragmentation to NH 3 + H, with a 9 kcal/mol barrier [2][3][4][5][6][7] restraining this fragmentation. For this reason, one clearly has to consider the possibility that the NH 4 moieties in (NH 4 ) 2 can fragment into 2NH 3 + H 2 or other species.…”

Section: Introductionmentioning

confidence: 99%

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On the Possibility of Mixed Rydberg-Valence Bonds

Boldyrev

Simons

1999

J. Phys. Chem. A

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Chemical bonding between the Rydberg molecule NH 4 and three alkali atoms Li, Na, and K, via their 2s, 3s, or 4s valence orbitals, is examined using flexible atomic orbital basis sets and high level ab initio methods. The results thus obtained suggest that (NH 4 )Na and (NH 4 )K should have large enough barriers to fragmentation (to (NH 3 ) plus the alkali hydride) to be detected experimentally if it can be formed, but suggest that (NH 4 )Li has such a small barrier to render it impossible or much more difficult to observe. For all three species, minimum-energy structures, local harmonic vibrational frequencies, and plots of the Rydberg-valence bonding orbitals are given. The activation barriers separating these structures from their (NH 4 ) plus alkali hydride fragments vary from 3 to 9 kcal/mol, while the energies required to dissociate to NH 4 plus an alkali atom range from 9 to 16 kcal/mol.

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An AB initio molecular orbital study of the ammonium radical

Cited by 37 publications

References 32 publications

Stability of the Rydberg Dimer (NH₄)₂

Stability of the Rydberg Dimer (NH₄)₂

Double-Rydberg molecular anions

On the Possibility of Mixed Rydberg-Valence Bonds

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An AB initio molecular orbital study of the ammonium radical

Cited by 37 publications

References 32 publications

Stability of the Rydberg Dimer (NH4)2

Stability of the Rydberg Dimer (NH4)2

Double-Rydberg molecular anions

On the Possibility of Mixed Rydberg-Valence Bonds

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Product

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Stability of the Rydberg Dimer (NH₄)₂

Stability of the Rydberg Dimer (NH₄)₂