An AB initio molecular orbital study of the ammonium radical (original) (raw)
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Ab initio study of the thermodynamic and kinetic stability of the ammonium radical
Chemical Physics, 1983
An mcreasmg mterest in the possible existence of the NH, radxai has emerged rn recent years In thus paper ue report an ab inmo UHF Cl study of the ammonmm radical. an mvestlgatlon of parts of the energ) surface around XH, and a theoretical predtctlon of the kmetlc parameters of the radxal formation and dlssociatlon reactlons anhm the frame\xork of the TST theory The ground state of the ammonium radxcal appears to be of the Rbdberg type. Its lomzatlon potennal 1s found to be 4 29 eV The NH., formation reactton from NH, + H, IS Lery shghtly evothermlc whereas the reactton from NH, + H IS sbghtly endothermx. We find a transition state of C,. symmetry for the cbssociatlon of NH, mto XH, + H. The msernon of H, Into NH, occurs accorchng to a tuo-step mechamsm uhose deterrnming step corresponds to the crossmg of a saddle pomt with C, symmetry previously obtamed m the stud) of the reaclmn NH2 + H2-NH, + H Fmall~. =e predwt for NH, and ND., hfetlmes of 0 1 and 1 4 gs respectl\ely * When ths paper uas subnutted for pubbcatlon one of the referees drew our attention to a recent paper bq XlcMastcr et al on "An ab mitlo hI0 study of the ammonium radical" [26] In the note added m proof we explam the relative posmon of the tuo concurrmg papers
Chemical Physics, 1996
Oscillator strengths and Einstein emission coefficients for NH4 and H2F Rydberg radicals have been calculated using the quantum defect orbital method. An estimate of the accuracy of this approach has been obtained by a comparison of the results with the data derived from more sophisticated ab initio methods. In several cases, in particular for H2F molecule, predictions of unknown transition probabilities have been given. The method proved to be a reliable and useful tool to estimate transition probabilities between molecular Rydberg states. Keywords: fiuoronium radical, ammonium radical, Rydberg states, electronic transitions, quantum defect orbital method. 0301-0104/96/$15.00 (~) 1996 Elsevier Science B.V. All rights reserved SSDI 030 1-0104(95)00370-3 1. Martin et al.
Vibronic Structure of the 3s and 3p Rydberg States of the Allyl Radical †
The Journal of Physical Chemistry A, 2010
Resonance-enhanced multiphoton ionization combined with electronic ground state depletion spectroscopy of jet-cooled allyl radicals (C 3 H 5) provides vibronic spectra of the 3s and 3p Rydberg states. Analysis of the vibronic structure following two-photon excitation of rovibrationally cold allyl radicals reveals transitions to the 3p z (2 A 1) Rydberg state with an electronic origin at 42230 cm-1. More than 40 transitions to vibrational levels in the partially overlapping spectra of the 3p y (2 B 2) Rydberg state and the 3s (2 A 1) Rydberg state are identified and reassigned on the basis of predictions from ab initio calculations and results and simulations of pulsed-field-ionization zero-kinetic-energy photoelectron spectra obtained recently using resonant multiphoton excitation via selected vibrational levels of these two Rydberg states (J. Chem. Phys. 2009, 131, 014304). Depletion spectroscopy reveals that the transition to the short-lived 3p x (2 B 1) Rydberg state in vicinity of three-state same symmetry conical intersections predicted theoretically carries most of the oscillator strength of these coupled 3s and 3p Rydberg states. The results allow for the first time to experimentally derive the energetic ordering of the 3p Rydberg states of the allyl radical.
The spectroscopy of high Rydberg states of ammonia
The Journal of chemical …, 1998
The spectroscopy of high Rydberg states of ammonia. [The Journal of Chemical Physics 108, 6667 (1998)]. Stephen R. Langford, Andrew J. Orr-Ewing, Ross A. Morgan, Colin M. Western, Michael NR Ashfold, Arjan Rijkenberg ...
Vibronic structure of the 3s Rydberg state of the 2-methylallyl radical
Journal of Molecular Spectroscopy, 2010
Resonance-enhanced multiphoton ionization combined with electronic ground state depletion spectroscopy of jet-cooled 2-methylallyl (C 4 H 7) radicals provides vibronic spectra of the 3s and 3p Rydberg states. Analysis of the vibronic structure following one-photon and two-photon excitation of rovibronically cold 2-methylallyl radicals and its isotopologues C 4 H 4 D 3 and C 4 D 7 reveals transitions to more than 30 vibrational levels in the 3s Rydberg state that are identified and reassigned on the basis of predictions from ab initio calculations and results from pulsed-field-ionization zero-kinetic-energy photoelectron spectra obtained with resonant multiphoton excitation via selected intermediate states. Depletion spectroscopy reveals transitions to short-lived 3p Rydberg states that have a large oscillator strength.
Electronic Spectra and Structures of Solvated NH4 Radicals, NH4(NH3)n (n = 1−8)
The Journal of Physical Chemistry A, 2002
Electronic spectra of ammoniated ammonium radicals, NH 4 (NH 3) n , produced through the photolysis of ammonia clusters, are investigated with a laser photodepletion spectroscopy. Vibrationaly resolved bands beginning at energy of 9305 (15 cm-1 are successfully assigned to NH 4 NH 3. These bands are ascribed to the 2 2 A-1 2 A transition derived from the 3p 2 F 2-3s 2 A 1 excitation of NH 4. A second group of bands beginning at energy 10073 (15 cm-1 is assigned to the 1 2 E-1 2 A transition. Electronic spectra of a series of NH 4 (NH 3) n (n) 1-8) are also recorded with low resolution in the energy region of 4500-16000 cm-1. A drastic decrease of the excitation energy from 15062 cm-1 for NH 4 to 5800 cm-1 for NH 4 (NH 3) 4 is observed, while no appreciable spectral change is found for n g 5. The large spectral change is ascribed to the spontaneous ionization of NH 4 in ammonia clusters. Successive binding energies of NH 4 (NH 3) n in the excited state are determined from the spectral band positions.
Theoretical and Computational Chemistry, 2007
A double Rydberg anion (DRA) consists of a stable cationic core and two electrons in a diffuse Rydberg orbital. These anions correspond to a local minimum on a potential energy surface where more stable isomers may exist. Experimental and theoretical works have contributed to a better understanding of the unusual electronic structure of these molecules. With electron propagator calculations and analysis of the electron localization function, some relationships between electronic structure and reactivity in DRAs are considered. J. Melin et al. HH bonding relationships between diffuse s functions. Such phase relationships and the predominance of diffuse s functions on hydrogens explained the sharpness of the corresponding photoelectron peak. This description also validated the use of the term double Rydberg anion (DRA), 2 4 for two electrons are found in a Rydberg-like orbital that is distributed on the periphery of a closed-shell cation, NH + 4 . Several theoretical works were published on other simple hydrides and, in addition to tetrahedral NH − 4 DRAs have been found 5−13 for C 3v OH − 3 and tetrahedral PH − 4 . Geometry optimizations of C 3v SH − 3 and linear structures of FH − 2 and ClH − 2 encountered transition states (TS) instead of DRA minima. The same study provided harmonic vibrational frequencies for NH − 4 OH − 3 , and PH − 4 . Recent calculations on NH 3 R − and OH 2 R − anions, where R = CH 3 NH 2 OH, and F, have identified other stable anions of this type. 14 Here, AH n substituents replace hydrogens from the parent species, tetrahedral NH − 4 , and C 3v OH − 3 . Dyson orbitals for electron detachments from stable anions such as NH 3 CH − 3 are delocalized over the periphery of the entire species. This result extends previous studies where large molecular cations were found to accommodate a diffuse, Rydberg electron that is spread over the periphery of the entire cationic kernel. 15 Covalent and ionic bonding that involves Rydberg-like orbitals has been explored as well. 16 Experiments with higher resolution on N 2 H −17 7 were quickly followed by electron propagator calculations 18 that confirmed the existence of an anion-molecule complex, H − NH 3 2 , and two DRAs with vertical electron-detachment energies placed symmetrically about the position of the low-energy peak in the NH − 4 spectrum. One of these N 2 H − 7 species is a complex consisting of the tetrahedral DRA and a coordinated ammonia molecule. The other features a hydrogen bond between two N atoms in a structure that resembles the N 2 H + 7 NH + 4 -NH 3 complex. The Dyson orbital for anion electron detachment in the latter isomer is localized on the three nonbridging hydrogens attached to the ammonium fragment's N atom. Vibrational satellites of each of the three vertical peaks also were assigned. Agreement of equally high quality was obtained for vibrational satellites seen in the NH − 4 spectrum. These works established the existence of a novel variety of electron pair in DRAs. Extensions of traditional electron pair concepts are clearly needed for these anions. The electron localization function (ELF) 19 is an interesting and robust descriptor of chemical bonding, which has been successfully applied to a wide variety of molecular systems. 20−24 This function, which is based on a topological analysis of a quantum function related to Pauli repulsion, describes the degree of localization (or delocalization) of electron pairs within the molecular space.
The ammonia dimer: new infrared-far infrared double resonance results
Chem Phys, 1995
From the results of an infrared-far infrared double resonance experiment on (NH 3) 2 complexes in a supersonic slit nozzle expansion, it was possible to characterize the tunneling dynamics, occurring within the ammonia dimer (Havenith et al., Chem. Phys. Letters 193 (1992) 261). In the current paper we present additional infrared-far infrared double resonance spectra. These confirm the former analysis and give a state specific explanation of the overall infrared spectrum of (NH 3) 2 as measured by Snels et al. (Chem. Phys. 115 (1987) 79). The interchange motion is shown to be quenched from 20 cm -1 in the ground state to less than 1 cm -1 in the infrared excited state. This confirms the assumption of Olthof et al. (J. Mol. Struct. THEOCHEM 307 (1994) 201) that the barrier for interchange tunneling is very small in (NH 3) 2.