Two Isomers of Protonated Isocyanic Acid: Evidence for an Ion-Molecule Pathway for HNCO ↔ HOCN Isomerization.
Ion-molecule reactions are thought to play a crucial role in the formation of metastable isomers, but relatively few protonated intermediates beyond HNCH(+) have been characterized at high spectral resolution. We present here laboratory measurements of the rotational spectra of protonated isocyanic acid in two isomeric forms, the ground state H2NCO(+) with C2v symmetry and a low-lying bent chain HNCOH(+), guided by coupled cluster calculations of their molecular structure. Somewhat surprisingly, HNCOH(+) is found to be more abundant than H2NCO(+), even though this metastable isomer is calculated to lie approximately 15-20 kcal/mol higher in energy. In the same way that HCNH(+) serves as a key intermediate in ion-molecule reactions that form HNC via dissociative electron recombination in cold dense interstellar molecular clouds, HNCOH(+) may play an analogous role in the conversion of HNCO to HOCN.
†Harvard-Smithsonian Center for Astrophysics, and School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, United States.
Valerio
V
Lattanzi
‡I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany.
Sven
S
Thorwirth
†Harvard-Smithsonian Center for Astrophysics, and School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, United States.
Carl A
CA
Gottlieb
†Harvard-Smithsonian Center for Astrophysics, and School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, United States.
Michael C
MC
McCarthy
bonding; molecular structure; quantum-chemical calculations; radio astronomy; rotational spectroscopy