Abstract
The production of complex molecules in ammonia–carbon dioxide ices is presumed to pass through species of formula H3N:CO2 with further addition of ammonia and carbon dioxide. One possible landmark, carbamic acid, H2NCOOH, has been implicated among the products of warming and irradiation of such ices. Experimental study of the IR spectra of residues has suggested the presence of related species, including weakly bound 1:1 and 2:1 complexes of ammonia with carbon dioxide, zwitterionic carbamic acid, ammonium carbamate, and the dimer of carbamic acid. We computed the energetics and vibrational spectra of these species as well as the complex between ammonia and carbamic acid for gas and condensed phases. By means of a new spectrum-matching scoring between computed and observed vibrational spectra, we infer species that are most probably present. The leading candidates are ammonium carbamate, the carbamic acid–ammonia complex, and the carbamic acid dimer.
Highlights
The production of complex molecules in ammonia–carbon dioxide ices is presumed to pass through species of formula H3 N:CO2 with further addition of ammonia and carbon dioxide
We suggest that the two computed frequencies establish a range that should capture the physical system’s value
Scoring in the same way as we evaluated matches among computed spectra, we find that the computed fundamental frequencies score 14.5 for the carbamic acid–ammonia complex; 11.5 for carbamic acid dimer, 11.0 for ammonium carbamate, and 9.5 for each of the three other structures, i.e., the zwitterionic carbamic acid and the 1:1 and 2:1 ammonia–carbon dioxide complexes
Summary
The production of complex molecules in ammonia–carbon dioxide ices is presumed to pass through species of formula H3 N:CO2 with further addition of ammonia and carbon dioxide. Experimental study of the IR spectra of residues has suggested the presence of related species, including weakly bound 1:1 and 2:1 complexes of ammonia with carbon dioxide, zwitterionic carbamic acid, ammonium carbamate, and the dimer of carbamic acid. We computed the energetics and vibrational spectra of these species as well as the complex between ammonia and carbamic acid for gas and condensed phases. Among the species of small molecules containing C, H, N, and O that may be formed on grains in ices are variants of carbamic acid, H2 NCOOH. Frasco [4] and Hisatsune [5] inferred from IR spectroscopy of the residue from VUV-irradiated and warmed ammonia–carbon dioxide ices that ammonium carbamate NH4 (+)H2 NCOO(−) is formed in the solid. Rodriguez-Lazcano et al [9] studied solid mixtures of ammonia and carbon monoxide by vapor deposition and hyperquenching on a cold plate with and without water, over a T range of
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
