The stability and specrta of isotopic forms of the ammonium radical: An ab initio CI study of the dissociation barrier

Kaspar, Johannes; Smith, Vedene H.; McMaster, Blair N.

doi:10.1016/0301-0104(85)80196-8

Cited by 35 publications

(30 citation statements)

References 27 publications

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“…Care should be taken with this value, as the calculation does not include zero-point vibrational energy and thermal corrections. Our results, however, are in good agreement with previous calculations [83][84][85][86][87]. The potential energy curves of ground and low-lying excited states for the dissociation of Rydberg NH 4 radicals into (NH 3 þ H) have been calculated with different levels of theory, namely MP2, MP4, CIPSI, SDCI and CCSDT.…”

Section: Wire Solvationsupporting

confidence: 80%

Controlling Excited‐State H‐Atom Transfer along Hydrogen‐Bonded Wires

Manca

Tanner

Leutwyler

2010

Hydrogen Bonding and Transfer in the Excited State

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Hydrogen-bonded wires are involved in a large variety of chemical and biological processes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The main reaction associated with hydrogen bonds is proton or H-atom transfer, in which a charge accompanies the transferring proton. A topic of specific interest is proton transport through transmembrane ion channels ('proton wires'), because many transmembrane proteins create, control and use the proton gradient across biological membranes. Hydrogen-bonded wires of water molecules have been identified in numerous membrane-spanning proteins, such as bacteriorhodopsin [17][18][19][20][21][22], the bacterial photosynthetic reaction centre of Rhodobacter sphaeroides [23], the transmembrane channel formed by gramicidin [24][25][26], cytochrome oxidase [27] and other voltage-gated proton channels [28]. The enzymes carbonic anhydrase [29,30] and alcohol dehydrogenase [30] also contain proton relays along chains of water molecules embedded in the interior of the protein. Recently, hydrogen-bonded ammonia wires have been detected in ammonia/ammonium transporter (Amt) transmembrane proteins, which are essential for nitrogen metabolism in all species [31,32]. The translocation mechanisms along these 'proton wires' have become fields of intense theoretical study [5-8, 24-26, 29, 30, 33, 34]. Most of the time, the assumed mechanism is Grotthuss type, after the inventor (1806) of the process. The modern version of the Grotthuss mechanism consists of successive transfers of an excess proton along a hydrogen-bonded wire. These transfers require sequences of reorientation of the wire molecules, which constitutes the rate-limiting step of the mechanism [35]. The excess proton diffuses through a hydrogen bond network via the formation/breaking of covalent bonds, as shown schematically in

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Section: Wire Solvationsupporting

confidence: 80%

Controlling Excited‐State H‐Atom Transfer along Hydrogen‐Bonded Wires

Manca

Tanner

Leutwyler

2010

Hydrogen Bonding and Transfer in the Excited State

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“…2; note, however, that the ionization energies for the dimer are significantly higher than shown there for the trimer). Previous ab initio calculations have shown [10] that the allowed 3d 2 T 2 ← 3s 2 A 1 and 4p 2 T 2 ← 3s 2 A 1 electronic transitions fall into the region 2.8 ... 3.4 eV, i.e. two-photon transitions with the probe photon energy of 3.1 eV are supported.…”

Section: Resultsmentioning

confidence: 90%

Ultrafast dynamics in ammonia clusters: analysis of protonated and unprotonated cluster ion signals

Freudenberg¹,

Radloff²,

Ritze³

et al. 1997

Z Phys D - Atoms, Molecules and Clusters

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The dynamics of ammonia clusters excited to thẽ A state with 160 fs laser pulses of 6.2 eV was studied by pump-probe experiments with a low probe photon energy of 3.1 eV. Protonated as well as unprotonated cluster ion signals have been observed. The time evolution of both species is characteristic of the intermediate rearrangement and fragmentation processes. The observations strongly support a previously developed kinetic model for this dynamics with the signal at long delay times>6 ps reflecting the species involved in the absorption dissociation ionization (ADI) mechanism. Strong evidence is found for the formation of an internally 'quasi protonated' excited state and of ammoniated NH 4 radicals.

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“…By contrast, the lowest excitation in CH4, C ls-4s (a, ), which is of pure Rydberg character, is obviously stable with respect to fragmentation, allowing the individual vibrational levels to be detected. This is also suggested by the Z+1 analogy: the NH4 radical, discovered experimentally by Herzberg [52] in 1981, shows a substantial barrier along the ground-state dissociation path [46]. For transitions to final states of e and t2 symmetry in NH3 and CH4, respectively, the JahnTeller coupling of electronic and nuclear motion will give rise to a dense manifold of final vibronic levels preventing the resolution of further spectral details.…”

Section: General Discussion and Conclusionmentioning

confidence: 90%

“…Indeed, bound states of the neutral radicals FH2, OH3, and NH4, referred to as Rydberg molecules, are known to exist from numerous experimental and theoretical studies (see, e.g. , Raynor and Herschbach [45] and Kaspar, Smith, and McMaster [46]). By analogy we may conclude that those K-shell excitations described as X 1s Rydberg transitions are stable, or at least metastable, with respect to fragmentation.…”

Section: General Discussion and Conclusionmentioning

confidence: 99%

K-shell excitation of the water, ammonia, and methane molecules using high-resolution photoabsorption spectroscopy

et al. 1993

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The K-shell excitation spectra of the hydrides water, ammonia, and methane have been measured in photoabsorption experiments using synchrotron radiation in combination with a high-resolution monochromator. For the case of methane, in particular, a wealth of spectral detail is observed which was not accessible in previous studies. The measured excitation energies and relative intensities compare well with values calculated using a complete second-order approximation for the polarization propagator. In order to determine the extent of admixing of valence excitations (i.e., transitions into virtual 0 orbitals) to the Rydberg manifolds, the X-H bond lengths have been varied in the calculations. In the case of H20, the two lowest-energy bands are due to the 0 1s-4a&/3s and 0 1s-2b2/3p transitions and have strong valence character; their width indicates that both excitations are dissociative. The NH3 and ND3 spectra are also broad which is not only due to possible dissociation but also to unresolved vibrational fine structure (v2 mode) and a Jahn-Teller instability. Valence character is concentrated in the lowest excited state in the Rydberg ns manifold, but is distributed more uniformly over the np(e) manifold. The weak dipole-forbidden C 1s -3s ( a & ) transition in CH4 and CD4 is accompanied by vibrational structure due to the v4 mode, indicating that it derives its intensity from vibronic coupling with the C 1s-3p(t2) transition. The structure on the latter band is extremely complicated due to Jahn-Teller coupling and cannot be assigned at present, as is the case for the Rydberg transitions at higher energies. The higher np Rydberg excitations contain considerable valence character. PACS number(s): 33.20.Rm 35.20. -i I. INTRQDUCTIDNE-shell excitation of the CH4, NH3, and H20 molecules has been studied in the past using both electronenergy-loss spectroscopy (EELS) [1 -4] and x-ray absorption spectroscopy [5 -9). Although the spectral resolution obtained with the latter technique has generally been rather modest and could not match that of EELS, recent advances in grazing-incidence monochromator design [10 -14] have resulted in a dramatic improvement of resolution with the "optical" approach. This has been shown in a number of high-resolution K-shell excitation spectra of small molecules reported recently (e.g. , ). In the present paper we describe measurements of the photoabsorption spectrum of gas phase H20, NH3, and CH4 in the near-E-edge region at a resolution sufficiently high to reveal directly the spectral line shape. To substantiate the assignments we have also calculated excitation energies and oscillator strengths using a polarization propagator method [20].In the virtual orbital spectrum of these hydrides and other saturated molecules one expects antibonding valence-type (cr ) orbitals which are the counterparts of the occupied bonding X-H orbitals. An important question is to what extent this antibonding valence character appears in the excitation spectrum. In most of the earlier E-shell studies on the h...

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The stability and specrta of isotopic forms of the ammonium radical: An ab initio CI study of the dissociation barrier

Cited by 35 publications

References 27 publications

Controlling Excited‐State H‐Atom Transfer along Hydrogen‐Bonded Wires

Controlling Excited‐State H‐Atom Transfer along Hydrogen‐Bonded Wires

Ultrafast dynamics in ammonia clusters: analysis of protonated and unprotonated cluster ion signals

K-shell excitation of the water, ammonia, and methane molecules using high-resolution photoabsorption spectroscopy

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