| Autor: |
Ichino T; JILA and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0440, USA., Wren SW, Vogelhuber KM, Gianola AJ, Lineberger WC, Stanton JF |
| Jazyk: |
angličtina |
| Zdroj: |
The Journal of chemical physics [J Chem Phys] 2008 Aug 28; Vol. 129 (8), pp. 084310. |
| DOI: |
10.1063/1.2973631 |
| Abstrakt: |
The 351.1 nm photoelectron spectrum of the cyclopentadienide ion has been measured, which reveals the vibronic structure of the X (2)E(1) (") state of the cyclopentadienyl radical. Equation-of-motion ionization potential coupled-cluster (EOMIP-CCSD) calculations have been performed to construct a diabatic model potential of the X (2)E(1) (") state, which takes into account linear Jahn-Teller effects along the e(2) (') normal coordinates as well as bilinear Jahn-Teller effects along the e(2) (') and ring-breathing a(1) (') coordinates. A simulation based on this ab initio model potential reproduces the spectrum very well, identifying the vibronic levels with linear Jahn-Teller angular momentum quantum numbers of +/-1/2. The angular distributions of the photoelectrons for these vibronic levels are highly anisotropic with the photon energies used in the measurements. A few additional weak photoelectron peaks are observed when photoelectrons ejected parallel to the laser polarization are examined. These peaks correspond to the vibronic levels for out-of-plane modes in the ground X (2)E(1) (") state, which arise due to several pseudo-Jahn-Teller interactions with excited states of the radical and quadratic Jahn-Teller interaction in the X (2)E(1) (") state. A variant of the first derivative of the energy for the EOMIP-CCSD method has been utilized to evaluate the strength of these nonadiabatic couplings, which have subsequently been employed to construct the model potential of the X (2)E(1) (") state with respect to the out-of-plane normal coordinates. Simulations based on the model potential successfully reproduce the weak features that become conspicuous in the 0 degrees spectrum. The present study of the photoelectron spectrum complements a previous dispersed fluorescence spectroscopic study by Miller and co-workers [J. Chem. Phys. 114, 4855 (2001); 114, 4869 (2001)] to provide a detailed account of the vibronic structure of X (2)E(1) (") cyclopentadienyl. The electron affinity of the cyclopentadienyl radical is determined to be 1.808+/-0.006 eV. This electron affinity and the gas-phase acidity of cyclopentadiene have been combined in a negative ion thermochemical cycle to determine the C-H bond dissociation energy of cyclopentadiene; D(0)(C(5)H(6),C-H)=81.5+/-1.3 kcal mol(-1). The standard enthalpy of formation of the cyclopentadienyl radical has been determined to be Delta(f)H(298)(C(5)H(5))=63.2+/-1.4 kcal mol(-1). |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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