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Title: Reinterpreting the infrared spectrum of H + HCN: Methylene amidogen radical and its coproducts

The methylene amidogen radical (H 2CN) plays a role in high-energy material combustion and extraterresterial atmospheres. Recent theoretical work has struggled to match experimental assignments for its CN and antisymmetric CH 2 stretching frequencies (ν 2 and ν 5), which were reported to occur at 1725 and 3103 cm –1. Herein, we compute the vibrational energy levels of this molecule by extrapolating quadruples-level coupled- cluster theory to the complete basis limit and adding corrections for vibrational anharmonicity. This level of theory predicts that ν 2 and ν 5 should occur at 1646 and 2892 cm –1, at odds with the experimental assignments. To investigate the possibility of defects in our theoretical treatment, we analyze the sensitivity of our approach to each of its contributing approximations. Our analysis suggests that the observed deviation from experiment is too large to be explained as an accumulation of errors, leading us to conclude that these transitions were misassigned. To help resolve this discrepancy, we investigate possible byproducts of the H + HCN reaction, which was the source of H 2CN in the original experiment. In particular, we predict vibrational spectra for cis-HCNH, trans-HCNH, and H 2CNH using high-level coupled-cluster computations. Based on these results,more » we reassign the transition at 1725 cm –1 to ν 3 of trans-HCNH, yielding excellent agreement. Supporting this identification, we assign a known contaminant peak at 886 cm –1 to ν 5 of the same conformer. Our computations suggest that the peak observed at 3103 cm –1, however, does not belong to any of the aforementioned species. To facilitate further investigation, we use structure and bonding arguments to narrow the range of possible candidates. Furthermore, these arguments lead us to tentatively put forth formaldazine [(H 2CN) 2] as a suggestion for further study, which we support with additional computations.« less
Authors:
 [1] ;  [1] ; ORCiD logo [2] ;  [3] ; ORCiD logo [4] ;  [1] ; ORCiD logo [1]
  1. Univ. of Georgia, Athens, GA (United States)
  2. Univ. of Georgia, Athens, GA (United States); Messiah College, Mechanicsburg, PA (United States)
  3. Univ. of Georgia, Athens, GA (United States); Federal Univ. of Sao Paulo, Sao Paulo (Brazil)
  4. Univ. of Georgia, Athens, GA (United States); Biola Univ., La Mirada, CA (United States)
Publication Date:
Grant/Contract Number:
SC0018412; SC0015512
Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 148; Journal Issue: 1; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Research Org:
Univ. of Georgia, Athens, GA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
OSTI Identifier:
1468296
Alternate Identifier(s):
OSTI ID: 1415508

Wiens, Avery E., Copan, Andreas V., Rossomme, Elliot C., Aroeira, Gustavo J. R., Bernstein, Olivia M., Agarwal, Jay, and Schaefer, Henry F.. Reinterpreting the infrared spectrum of H + HCN: Methylene amidogen radical and its coproducts. United States: N. p., Web. doi:10.1063/1.5004984.
Wiens, Avery E., Copan, Andreas V., Rossomme, Elliot C., Aroeira, Gustavo J. R., Bernstein, Olivia M., Agarwal, Jay, & Schaefer, Henry F.. Reinterpreting the infrared spectrum of H + HCN: Methylene amidogen radical and its coproducts. United States. doi:10.1063/1.5004984.
Wiens, Avery E., Copan, Andreas V., Rossomme, Elliot C., Aroeira, Gustavo J. R., Bernstein, Olivia M., Agarwal, Jay, and Schaefer, Henry F.. 2018. "Reinterpreting the infrared spectrum of H + HCN: Methylene amidogen radical and its coproducts". United States. doi:10.1063/1.5004984.
@article{osti_1468296,
title = {Reinterpreting the infrared spectrum of H + HCN: Methylene amidogen radical and its coproducts},
author = {Wiens, Avery E. and Copan, Andreas V. and Rossomme, Elliot C. and Aroeira, Gustavo J. R. and Bernstein, Olivia M. and Agarwal, Jay and Schaefer, Henry F.},
abstractNote = {The methylene amidogen radical (H2CN) plays a role in high-energy material combustion and extraterresterial atmospheres. Recent theoretical work has struggled to match experimental assignments for its CN and antisymmetric CH2 stretching frequencies (ν2 and ν5), which were reported to occur at 1725 and 3103 cm–1. Herein, we compute the vibrational energy levels of this molecule by extrapolating quadruples-level coupled- cluster theory to the complete basis limit and adding corrections for vibrational anharmonicity. This level of theory predicts that ν2 and ν5 should occur at 1646 and 2892 cm–1, at odds with the experimental assignments. To investigate the possibility of defects in our theoretical treatment, we analyze the sensitivity of our approach to each of its contributing approximations. Our analysis suggests that the observed deviation from experiment is too large to be explained as an accumulation of errors, leading us to conclude that these transitions were misassigned. To help resolve this discrepancy, we investigate possible byproducts of the H + HCN reaction, which was the source of H2CN in the original experiment. In particular, we predict vibrational spectra for cis-HCNH, trans-HCNH, and H2CNH using high-level coupled-cluster computations. Based on these results, we reassign the transition at 1725 cm–1 to ν3 of trans-HCNH, yielding excellent agreement. Supporting this identification, we assign a known contaminant peak at 886 cm–1 to ν5 of the same conformer. Our computations suggest that the peak observed at 3103 cm–1, however, does not belong to any of the aforementioned species. To facilitate further investigation, we use structure and bonding arguments to narrow the range of possible candidates. Furthermore, these arguments lead us to tentatively put forth formaldazine [(H2CN)2] as a suggestion for further study, which we support with additional computations.},
doi = {10.1063/1.5004984},
journal = {Journal of Chemical Physics},
number = 1,
volume = 148,
place = {United States},
year = {2018},
month = {1}
}