Microwave spectrum, large-amplitude motions, and ab initio calculations for N₂O₅

authored by: J. U. Grabow, A. M. Andrews, G. T. Fraser, K. K. Irikura, R. D. Suenram, F. J. Lovas, W. J. Lafferty, J. L. Domenech
Abstract: The rotational spectrum of dinitrogen pentoxide (N₂O₅) has been investigated between 8 to 25 GHz at a rotational temperature of ∼2.5 K using a pulsed-molecular-beam Fourier-transform microwave spectrometer. Two weak b-dipole spectra are observed for two internal-rotor states of the molecule, with each spectrum poorly characterized by an asymmetric-rotor Hamiltonian. The observation of only 6-type transitions is consistent with the earlier electron-diffraction results of McClelland et al. [J. Am. Chem. Soc. 105, 3789 (1983)] which give a C₂ symmetry molecule with the b inertial axis coincident with the C₂ axis. Analysis of the ¹⁴N nuclear hyperfine structure demonstrates that the two nitrogen nuclei occupy either structurally equivalent positions or are interchanging inequivalent structural positions via tunneling or internal rotation at a rate larger than ∼1 MHz. For the two internal rotor states, rotational levels with K_a + K_c even have I_N=0, 2, while levels with K_a + K_c odd have I_N= 1, where I_N is the resultant nitrogen nuclear spin. This observation establishes that the equilibrium configuration of the molecule has a twofold axis of symmetry. Guided by ab initio and dynamical calculations which show a planar configuration is energetically unfavorable, we assign the spectrum to the symmetric and antisymmetric tunneling states of a C₂ symmetry N₂O₅ with internal rotation tunneling of the two NO₂ groups via a geared rotation about their respective C₂ axes. Because of the Bose-Einstein statistics of the spin-zero oxygen nuclei, which require that the rotational-vibrational-tunneling wave functions be symmetric for interchange of the O nuclei, only four of the ten vibrational-rotational-tunneling states of the molecule have nonzero statistical weights. Model dynamical calculations suggest that the internal-rotation potential is significantly more isotropic than implied by the electron-diffraction analysis.
Organisation(s): Institute of Physical Chemistry and Electrochemistry
External Organisation(s): National Institute of Standards and Technology (NIST)
Spanish National Research Council (CSIC)
Institute for Defense Analysis (IDA)
Type: Article
Journal: Journal of Chemical Physics
Volume: 105
Pages: 7249-7262
No. of pages: 14
ISSN: 0021-9606
Publication date: 1996
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: General Physics and Astronomy, Physical and Theoretical Chemistry
Electronic version(s): https://doi.org/10.1063/1.472586 (Access: Unknown)

BibTeX

@article{040c1717756a4b9ca305c5f86d295efd,
title = "Microwave spectrum, large-amplitude motions, and ab initio calculations for N2O5",
abstract = "The rotational spectrum of dinitrogen pentoxide (N2O5) has been investigated between 8 to 25 GHz at a rotational temperature of ∼2.5 K using a pulsed-molecular-beam Fourier-transform microwave spectrometer. Two weak b-dipole spectra are observed for two internal-rotor states of the molecule, with each spectrum poorly characterized by an asymmetric-rotor Hamiltonian. The observation of only 6-type transitions is consistent with the earlier electron-diffraction results of McClelland et al. [J. Am. Chem. Soc. 105, 3789 (1983)] which give a C2 symmetry molecule with the b inertial axis coincident with the C2 axis. Analysis of the 14N nuclear hyperfine structure demonstrates that the two nitrogen nuclei occupy either structurally equivalent positions or are interchanging inequivalent structural positions via tunneling or internal rotation at a rate larger than ∼1 MHz. For the two internal rotor states, rotational levels with Ka + Kc even have IN=0, 2, while levels with Ka + Kc odd have IN= 1, where IN is the resultant nitrogen nuclear spin. This observation establishes that the equilibrium configuration of the molecule has a twofold axis of symmetry. Guided by ab initio and dynamical calculations which show a planar configuration is energetically unfavorable, we assign the spectrum to the symmetric and antisymmetric tunneling states of a C2 symmetry N2O5 with internal rotation tunneling of the two NO2 groups via a geared rotation about their respective C2 axes. Because of the Bose-Einstein statistics of the spin-zero oxygen nuclei, which require that the rotational-vibrational-tunneling wave functions be symmetric for interchange of the O nuclei, only four of the ten vibrational-rotational-tunneling states of the molecule have nonzero statistical weights. Model dynamical calculations suggest that the internal-rotation potential is significantly more isotropic than implied by the electron-diffraction analysis.",
author = "Grabow, {J. U.} and Andrews, {A. M.} and Fraser, {G. T.} and Irikura, {K. K.} and Suenram, {R. D.} and Lovas, {F. J.} and Lafferty, {W. J.} and Domenech, {J. L.}",
year = "1996",
doi = "10.1063/1.472586",
language = "English",
volume = "105",
pages = "7249--7262",
journal = "Journal of Chemical Physics",
issn = "0021-9606",
publisher = "American Institute of Physics",
number = "17",
}

Microwave spectrum, large-amplitude motions, and ab initio calculations for N2O5

Microwave spectrum, large-amplitude motions, and ab initio calculations for N₂O₅