Rydberg–Valence Interactions in Monoolefins: Dispersing Electronic Properties in 1,1′‐Bicyclohexylidene

Abstract

Disentangling the embrace: Calculations on the electronic structure of 1,1′‐bicyclohexylidene (shown in the graphic) indicate that electronic coupling of the excited ππ* valence state with Rydberg states lies at the basis of the hitherto poorly understood presence of two low‐lying electronic states with valencelike properties. States with similar characteristics are predicted for the entire class of monoolefins.

Rydberg or Valence? The Long‐Standing Question in the UV Absorption Spectrum of 1,1′‐Bicyclohexylidene

“…The assignment of the pp* state as the high-energy band (6.82 eV) disagrees with previous theoretical assignments; [20][21][22][23][24] however, it successfully explains the presence of the two bands in solid state as vibrational structure of the valence pp* transition. As stated in refs.…”

“…At the CASSCF level of theory the first 1 1 B u state is clearly a p3s R excitation (76 %), while the second 2 1 B u state is a mixture of a pp* excitation (54 %) and a p-Rydberg transition (35 %). This mixture is an artifact of the CASSCF method, as it also appears in CIS [24] or in other methods. [13] Other erratic valence-Rydberg contributions can also be observed in the 4 1 B u and 5 1 B u states (a reason why five roots are necessary to calculate the pp* state).…”

“…these same authors proposed [24] a mixing of the valence state with the p3d Rydberg manifold. Not surprisingly, an increase in the diffuseness of the basis set led to increasing Rydberg-valence mixing, something that a treatment practically lacking electronic correlation effects cannot solve.…”

“…[20][21][22][23][24] A summary of all diverse experimental and theoretical assignments up to the present is collected in Table 1. Allan, Snyder, and Robin reinvestigated the electronic excitations of BCH with photoelectron, electron impact, and multiphoton ionization spectroscopy, [18] concluding that the structured bands of…”

Isolated Building Blocks of Photonic Materials: High-Resolution Excited-State Photoelectron Spectroscopy of Jet-Cooled Tetramethylethylene and 1,1‘-Bicyclohexylidene

“…Bearing in mind that alkylation of the CdC bond has a smaller effect on the excitation energy of the (π,π*) valence state, 23 the energy gap between the (π,π*) valence state and the (π,3d) Rydberg manifold is expected to be smaller in BCH and TME than in ethylene, and thus Rydberg-valence mixing to be increased in the former compounds. A recent ab initio study on the excited states of a wide range of alkylated mono-olefins ranging from propylene to BCH 75 has provided support for such an enhancement of Rydberg-valence coupling, and shows evidence for strong Rydberg-valence mixing in TME and BCH.…”