Infrared spectroscopy of [H₂O–X_n]⁺(n= 1–3, X = N₂, CO₂, CO, and N₂O) radical cation clusters: competition between hydrogen bond and hemibond formation of the water radical cation

Abstract

The water radical cation H2O+ is an important intermediate in radiation chemistry and radiobiology, and its role in radical reactions has recently attracted much attention. However, knowledge of H2O+ remains...

Correlation of the Charge Resonance Interaction with Cluster Conformations Probed by Electronic Spectroscopy of Dimer Radical Cations of CO2 and CS2 in a Cryogenic Ion Trap

“…The overlap integral S in eq is often considered negligible for simple estimation of the CR interaction. Accordingly, the roughly estimated binding energy of [(CO 2 ) 2 ] +• and [(CS 2 ) 2 ] +• was ∼7000 cm –1 , which is significantly larger than that of heterodimeric radical cations, such as [CO 2 –X] + (X = H 2 O and CH 3 OH). , This result reflects the degree of charge delocalization in the dimer cations; a smaller difference between the ionization potentials of two molecular components causes efficient charge delocalization and, thus, larger CR interactions …”

“…In this bonding scheme, the total charge is distributed across the components. Because the formal bond order in this bonding mode is 0.5 (Scheme ), such bonds are often referred to as semi-covalent bonds or hemibonds. − Remarkably, the electronic transition from σ to σ* orbitals in this bonding scheme, known as the CR transition, leads to a prominent absorption band in the near-infrared–visible region (CR band). − Consequently, the spectroscopic characterizations have attracted considerable attention. − Particularly, when the corresponding electronic ground and excited states (Ψ ± ) are described as Ψ ± = [ψ(M A + )ψ(M B ) ± ψ(M A )ψ(M B + )]/(2 ± 2 S ) 1/2 , the CR transition energy ( E T ) is directly related to the binding energy between the component molecules in the dimer ions ( E B ), as illustrated in the following relationship (eq ): E normalT = 2 E normalB 1 − S Here, S represents the overlap integral between the constituent molecules.…”