Valence orbital response to pseudorotation of tetrahydrofuran: A snapshot using dual space analysis

The pseudorotation of tetrahydrofuran (THF) (C4 H8 O) has been studied using density functional theory, with respect to the valence orbital responses to the ionization potentials and to orbital electron and momentum distributions. Three conformations of THF, the global minimumstructure Cs, local minimum structure C2, and a transition state structure C1, which arecharacteristic configurations on the potential energy surface, are examined using the SAOPet-pVQZ//B3LYP6-311++ G* models with the aforementioned dual space analysis. It is noted in the ionization energy spectra that the minimum structures Cs and C2 are not directly connected by pseudorotation, but through the transition state structure C1. As a result, some orbitals of the Cs conformer are able to 'correlate' to orbitals of the C2 conformer without a strict symmetry constraint, i.e., orbital 7 a′ of the Cs conformer is correlated to orbital 5b of the C2 conformer. It is also noted that although the valence orbital ionization potentials are not significantly altered by the pseudorotation of THF, their spectra (mainly due to excitation) are quite different indeed. Detailed orbital analysis based on dual space analysis is given. The valence orbital behavior of the conformations is orbital dependent. It can be approximately divided into three groups: the 'signature group' is associated with orbitals experiencing significant changes. The frontier orbitals are in this group. The 'nearly identical group' includes orbitals without apparent changes across the conformations. Most of the orbitals showing a certain degree of distortion during the pseudorotation process belong to the third group. The present study demonstrates that a comprehensive understanding of the pseudorotation of THF and its dynamics requires multidimensional information and that the information gained from momentum space is complementary to that from the more familiar coordinate space.