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Title: NEW GROUND-STATE MEASUREMENTS OF ETHYL CYANIDE

Abstract

The spectrum of ethyl cyanide, or propionitrile (CH{sub 3}CH{sub 2}CN), has been repeatedly observed in the interstellar medium with large column densities and surprisingly high temperatures in hot core sources. The construction of new, more sensitive, observatories accessing higher frequencies such as Herschel, ALMA, and SOFIA have made it important to extend the laboratory data for ethyl cyanide to coincide with the capabilities of the new instruments. We report extensions of the laboratory measurements of the rotational spectrum of ethyl cyanide in its ground vibrational state to 1.6 THz. A global analysis of the ground state, which includes all of the previous data and 3356 newly assigned transitions, has been fitted to within experimental error to J = 132, K = 36, using both Watson A-reduced and Watson S-reduced Hamiltonians.

Authors:
; ; ;  [1]
  1. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States), E-mail: Carolyn.S.Brauer@jpl.nasa.gov
Publication Date:
OSTI Identifier:
21301599
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal, Supplement Series; Journal Volume: 184; Journal Issue: 1; Other Information: DOI: 10.1088/0067-0049/184/1/133; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ASTROPHYSICS; CATALOGS; CYANIDES; GLOBAL ANALYSIS; GROUND STATES; HAMILTONIANS; SPECTRA; VIBRATIONAL STATES

Citation Formats

Brauer, Carolyn S., Pearson, John C., Drouin, Brian J., and Yu, Shanshan. NEW GROUND-STATE MEASUREMENTS OF ETHYL CYANIDE. United States: N. p., 2009. Web. doi:10.1088/0067-0049/184/1/133; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Brauer, Carolyn S., Pearson, John C., Drouin, Brian J., & Yu, Shanshan. NEW GROUND-STATE MEASUREMENTS OF ETHYL CYANIDE. United States. doi:10.1088/0067-0049/184/1/133; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Brauer, Carolyn S., Pearson, John C., Drouin, Brian J., and Yu, Shanshan. Tue . "NEW GROUND-STATE MEASUREMENTS OF ETHYL CYANIDE". United States. doi:10.1088/0067-0049/184/1/133; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
@article{osti_21301599,
title = {NEW GROUND-STATE MEASUREMENTS OF ETHYL CYANIDE},
author = {Brauer, Carolyn S. and Pearson, John C. and Drouin, Brian J. and Yu, Shanshan},
abstractNote = {The spectrum of ethyl cyanide, or propionitrile (CH{sub 3}CH{sub 2}CN), has been repeatedly observed in the interstellar medium with large column densities and surprisingly high temperatures in hot core sources. The construction of new, more sensitive, observatories accessing higher frequencies such as Herschel, ALMA, and SOFIA have made it important to extend the laboratory data for ethyl cyanide to coincide with the capabilities of the new instruments. We report extensions of the laboratory measurements of the rotational spectrum of ethyl cyanide in its ground vibrational state to 1.6 THz. A global analysis of the ground state, which includes all of the previous data and 3356 newly assigned transitions, has been fitted to within experimental error to J = 132, K = 36, using both Watson A-reduced and Watson S-reduced Hamiltonians.},
doi = {10.1088/0067-0049/184/1/133; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
journal = {Astrophysical Journal, Supplement Series},
number = 1,
volume = 184,
place = {United States},
year = {Tue Sep 01 00:00:00 EDT 2009},
month = {Tue Sep 01 00:00:00 EDT 2009}
}
  • There is a general consensus that many of the unidentified features in astrophysical spectra are due to low lying excited vibrational and torsional states of a few molecules-commonly referred to as the astrophysical weeds. This is a challenging spectroscopic problem not only because there are many such states, but also because these states are often highly perturbed and difficult to analyze. We have previously described an alternative approach based on experimental, intensity-calibrated spectra taken at many temperatures. In this paper, we describe the procedures and results obtained with this approach for ethyl cyanide, strategies for archiving and disseminating these results,more » and the prospects for using these results to reduce the confusion limit in the powerful new observatories that are coming online.« less
  • Patterns of the shifts in bridging cyanide-stretching frequencies have been examined in several fully saturated, {mu}-cyano, bi- or trimetallic transition-metal donor-acceptor (D/A) complexes. An earlier inference that the bridging ligand nuclear and the D/A electronic coordinates are entangled is unequivocally demonstrated by the 32 cm{sup {minus}1} lower frequency of {nu}{sub CN} for (NH{sub 3}){sub 5}Cr(CNRu(NH{sub 3}){sub 5}){sup 4+} than for the cyanopentaamminechromium(III) parent. This contrasts to the 41 cm{sup {minus}1} increase in {nu}{sub CN} upon ruthenation of (NH{sub 3}){sub 5}RhCN{sup 2+}. More complex behavior has been found for cis and trans trimetallic, donor-acceptor complexes. The symmetric combination of CN{sup {minus}}more » stretching frequencies in trans-Cr{sup III}(MCL)(CNRu{sup II}(NH{sub 3}){sub 5}){sub 2}{sup 5+} complexes (MCL = a tetraazamacrocyclic ligand) shifts 100--140 cm{sup {minus}1} to lower frequency, and the antisymmetric combination shifts less than about 30 cm{sup {minus}1}. This contrast in the shifts of the symmetric and the antisymmetric combinations of the CN stretches persists even in a trans complex with no center of symmetry. Two CN stretches have also been resolved in an analogous cis complex, and both shift to lower frequency by about 60 cm{sup {minus}1}. The net shift, summed over all the CN-stretching frequencies, is about the same for the bis-ruthenates of related dicyano complexes. A simple, symmetry-adapted perturbation theory treatment of the coupled vibrations is employed to deal with the opposing effects of the kinematic shifts ({delta}) of {nu}{sub CN} to higher frequency, expected in the absence of D/A coupling, and shifts ({line{underscore}integral}) of {nu}{sub CN} to lower frequency that occur when D/A coupling is large. The Rh(III)- and Cr(III)-centered complexes correspond to different limits of this model: {delta} {gt} {line{underscore}integral} and {delta} {lt} {line{underscore}integral}, respectively. When referenced by means of this model to complexes with Rh(III) acceptors, the shifts in trimetallic complexes, summed over the symmetric and antisymmetric combinations of CN stretches, are about twice those of bimetallic complexes. Similarly referenced and summed over all bridging CN frequencies, the shifts of {nu}{sub CN} to lower energies are proportional to the oscillator strength of the electronic, donor-acceptor charge-transfer transition. The simplest interpretation of this correlation is that the donor-acceptor coupling in these systems is a function of the nuclear coordinates of the bridging ligand. This behavior of these complexes is semiquantitatively consistent with expectation for CN{sup {minus}}-mediated vibronic (pseudo-Jahn-Teller) coupling of neighboring donors and acceptors, and the observed Ru{sup II}/CN{sup {minus}} CT absorption parameters can be used in a simple, semiclassical vibronic model to predict shifts in {nu}{sub CN} that are in reasonable agreement with those observed.« less
  • A number of lines of the nu/sub 3/ band of hydrogen cyanide have been detected in solar absorption spectra recorded near sunrise and sunset at Kitt Peak National Observatory (elevation 2095 m) with a 0.01-cm/sup -1/ resolution Fourier transform spectrometer. Analysis of two of the strongest and best isolated lines has led to a value of 2.73 x 10/sup 15/ molecules cm/sup -2/ for the vertical column abundance of HCN above Kitt Peak. The accuracy of this value is estimates as +/-25%. This result, combined with the stratospheric concentration of HCN derived by Coffey, Mankin, and Cicerone (1981), yields 166more » parts per trillion by volume for the average mixing ratio of HCN between 2 and 12 km. This is the first determination of the HCN concentration in the nonurban troposphere. 26 references, 5 figures, 3 tables.« less
  • Ab initio SCF calculations on the ground state of free base porphine, chlorin, and ethyl pheophorbide a have been carried out using the molecular fragment procedure. Molecular orbital energies and ordering, and the correlations of specific orbitals among the molecules studied, have been examined in detail. Ionization potentials have been estimated, and the first ionization potentials are 6.8, 6.4, and 6.4 eV for porphine, chlorin, and ethyl pheophorbide a, respectively. The calculations show the expected approximate separation of the HOMO, HOMO--1, LUMO, and LUMO + 1 from the remainder of the MO manifold in keeping with the ''four orbital'' model,more » and isodensity contour plots of occupied and unoccupied molecular orbitals indicate a striking similarity in the ''shapes'' of these orbitals in all three molecules. Charges and bond orders have been examined. In porphine and chlorin, the bonding picture includes an extended ..pi.. system whose path of conjugation involves the atoms of the interior of the macrocycle, including the nitrogens and methine carbons. Also, relatively localized ..pi.. bonds are found between the exterior carbon atoms of the pyrrole moieties. In ethyl pheophorbide a, the ..pi.. bonds of the keto carbonyl of ring V and the vinyl group of ring I are mostly localized, but the path of conjugation within the macrocycle is somewhat less clear. Finally, molecular electrostatic isopotential maps have been constructed and an analysis of the long-range electrostatic field and its relationship to intermolecular interactions is discussed.« less
  • Ab initio SCF-MO calculations of magnesium porphine, magnesium chlorin, ethyl chlorophyllide a, and the ethyl chlorophyllide a.H/sub 2/O adduct have been carried out using the molecular fragment procedure. Molecular orbital energies and ordering, and the correlation of specific orbitals among the molecules, have been examined in detail. The calculations show the expected approximate separation of the HOMO, HOMO--1, LUMO, and LUMO + 1 from the remainder of the MO manifold as was also seen for the corresponding free bases, in keeping with the four-orbital model. Isodensity contour plots of occupied and unoccupied molecular orbitals indicate substantial similarities, both to eachmore » other and to the corresponding magnesium-free molecules. Ionization potential estimates are consistent with the greater ease of electrochemical oxidation of the magnesium-containing species in comparison to their corresponding free bases. In magnesium porphine and magnesium chlorin, the bonding picture that emerges is one of localized ..pi.. bonds in the periphery of the pyrrolic rings, with a path of conjugation which includes the methine carbons and the ''inner parts'' of the pyrrolic rings. Except for the approximate symmetrization of the electron populations of the pyrrolic nitrogens, a considerable number of similarities exist between the magnesium and corresponding free base species. Examination of the ethyl chlorophyllide a.H/sub 2/O adduct indicates that very little change in the electronic structure of ethyl chlorophyllide a occurs upon H/sub 2/O addition, except in the region of the magnesium nucleus. Finally, molecular electrostatic isopotential maps have been constructed and an analysis of the long-range electrostatic field and its relationship to intermolecular interactions is discussed.« less