Photoelectron spectroscopy of HCCN- and HCNC- reveals the quasilinear triplet carbenes, HCCN and HCNC

Nimlos, M. R., Davico, G., Geise, C. M., Wenthold, P. G., Lineberger, W. C., Blanksby, Stephen J., Hadad, C. M., Petersson, G. A., & Ellison, G. B. (2002) Photoelectron spectroscopy of HCCN- and HCNC- reveals the quasilinear triplet carbenes, HCCN and HCNC. Journal of Chemical Physics, 117(9), pp. 4323-4339.

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Negative ion photoelectron spectroscopy has been used to study the HCCN- and HCNC- ions. The electron affinities (EA) of cyanocarbene have been measured to be EA(HCCN (X) over tilde (3)Sigma(-)=2.003+/-0.014 eV and EA(DCCN (X) over tilde (3)Sigma(-))=2.009+/-0.020 eV. Photodetachment of HCCN- to HCCN (X) over tilde (3)Sigma(-) shows a 0.4 eV long vibrational progression in nu(5), the H-CCN bending mode; the HCCN- photoelectron spectra reveal excitations up to 10 quanta in nu(5). The term energies for the excited singlet state are found to be T-0(HCCN (a) over tilde (1)A('))=0.515+/-0.016 eV and T-0(DCCN (a) over tilde (1)A('))=0.518+/-0.027 eV. For the isocyanocarbene, the two lowest states switch and HCNC has a singlet ground state and an excited triplet state. The electron affinities are EA(HCNC (X) over tilde (1)A('))=1.883+/-0.013 eV and EA((X) over tilde (1)A(') DCNC)=1.877+/-0.010 eV. The term energy for the excited triplet state is T-0(HCNC (a) over tilde (3)A("))=0.050+/-0.028 eV and T-0(DCNC (a) over tilde (3)A("))=0.063+/-0.030 eV. Proton transfer kinetics in a flowing afterglow apparatus were used to re-measure the enthalpy of deprotonation of CH3NC to be Delta(acid)H(298)(CH3NC)=383.6+/-0.6 kcal mol(-1). The acidity/EA thermodynamic cycle was used to deduce D-0(H-CHCN)=104+/-2 kcal mol(-1) [Delta(f)H(0)(HCCN)=110+/-4 kcal mol(-1)] and D-0(H-CHNC)=106+/-4 kcal mol(-1) [Delta(f)H(0)(HCNC)=133+/-5 kcal mol(-1)]. (C) 2002 American Institute of Physics.

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ID Code: 71512
Item Type: Journal Article
Refereed: Yes
Keywords: gas-phase ion, laser magnetic-resonance, set model chemistry, carbanion, spectroscopy, equilibrium geometry, excitation-energies, bending, vibration, bond-energies, atomic oxygen, thermochemistry
DOI: 10.1063/1.1496473
ISSN: 1089-7690 (online) 0021-9606 (print)
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2002 American Institute of Physics
Deposited On: 13 May 2014 04:24
Last Modified: 13 May 2014 04:24

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