Infrared Signatures of the NCCO Radical.
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Peter R. Schreiner, Hans Peter Reisenauer, Edit Mátyus, Attila G. Császár, Ali Siddiqi, Andrew C. Simmonett, and Wesley D. Allen Phys. Chem. Chem. Phys. 2009, 11, 10385-10390. Download |
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The first definitive infrared signatures of the elusive NCCO radical have been measured using a microwave discharge technique combined with low-temperature matrix-isolation spectroscopy, resulting in a consistent set of vibrational assignments for six isotopologues. The infrared spectra of these NCCO isotopologues were concomitantly established by rigorous variational nuclear-motion computations based on a high-level coupled-cluster quartic vibrational force field [ROCCSD(T)/cc-pCVQZ] and cubic dipole field [ROCCSD/cc-pCVTZ]. Our experimental and theoretical results for NCCO overturn the vibrational assignments in a NIST-JANAF compilation and those from a recent two-dimensional cross-spectral correlation analysis. For the parent isotopologue at 11 K in a nitrogen matrix, we find the signature bands n2(CO str.) = 1889.2 cm-1 and n3(CC str.) = 782.0 cm-1. Our variational vibrational computations reveal strong mixing of the n3 stretching fundamental and the n4+n5 bending combination level for all isotopologues. These Fermi resonances manifest a clear breakdown of the simple normal-mode picture of molecular vibrations at low energies. |