On the electronic structure of the ground state of cyclopentoxy. The case for a two coupled state description

Abstract

Previous descriptions of the cyclopentoxy radical have considered the ground state as an isolated electronic state; however, the doublet ground and first excited states of the cyclopentoxy radical arise from three electrons in the oxygen 2pπ orbitals, yielding states that may not be adequately described by a single state model. In this work, a prelude to the determination of the photoelectron spectrum of cyclopentoxide, the electronic structure of the ground and first excited state of cyclopentoxy is studied. Both axial and equatorial structures are considered. The ground state is found to have an axial configuration. Conical intersections on the ground and excited state potential energy surfaces in both axial and equatorial nuclear configurations are found, with the minimum energy axial (equatorial) conical intersection lying within ~515 (260) cm-1 of the axial (equatorial) ground state minimum. The barriers to axial-equatorial interconversion and to ring opening are estimated. The implications for the simulation of the cyclopentoxide photoelectron spectrum are discussed.

Construction of Quasi-diabatic Hamiltonians That Accurately Represent ab Initio Determined Adiabatic Electronic States Coupled by Conical Intersections for Systems on the Order of 15 Atoms. Application to Cyclopentoxide Photoelectron Detachment in the Full 39 Degrees of Freedom

“…Construction of H d . The electronic structure description adopted here for C 5 H 9 O is a previously reported 56 MRCI with single and double excitations (MRCISD), with 6 frozen core orbitals, 15 doubly occupied orbitals, and a 5electron 3-orbital active space. The atomic orbital basis set is cc-pVTZ 57 for the oxygen and the carbons, and cc-pVDZ 58 for the hydrogens.…”

Photoelectron Spectroscopy of the Aminomethoxide Anion, H2C(NH2)O–

“…As an open-shell species with the radical center located on the oxygen, complicated further by some radicals possessing high symmetry, alkoxy radicals often have complex electronic structure making it difficult to fully characterize these molecules spectroscopically. Both their high reactivity and challenging electronic structure have motivated investigations of alkoxy radicals using a variety of experimental and theoretical methods. − Experimentally, alkoxy radicals have been studied in the gas phase mainly via spectroscopic techniques. ,− Theoretically, the electronic structure of small alkoxy radicals have been investigated with a focus on Jahn–Teller interactions, spin–orbit splittings, and vibronic couplings. − …”

Compact Bases for Vibronic Coupling in Spectral Simulations: The Photoelectron Spectrum of Cyclopentoxide in the Full 39 Internal Modes

“…The CISD expansion is composed of 7 634 278 CSFs. All electronic structure data used in this work were reported previously and employed the COLUMBUS − suite of programs. The MRCISD evinces a 1,2 2 A minimum energy crossing (MEX) structure for C 5 H 9 O that deviates slightly from its ground state minimum (MIN) and is only 0.064 eV higher in energy (see Table ).…”