Energy component analysis of the Jahn–Teller effect in the methane radical cation

Abstract

Extensive configuration-interaction calculations with double-zeta plus polarization and near triple-zeta plus polarization basis sets are used to analyze the Jahn–Teller (JT) effect in the methane radical cation. Energy component analysis shows that the Jahn–Teller effect leads to a decrease in the expectation value of the electron-nuclear attraction energy, an increase in the expectation value of the interelectronic repulsion energy, and an increase in the internuclear repulsion energy. These observations are consistent with a contraction of the electron cloud. The dominant factor in the −0.0550 hartree Jahn–Teller distortion (Td→C2v) in CH+4 is the −0.5262 hartree change in the electron–nuclear attraction energy. The differences in all energy components are large in relation to the JT distortion. Interelectronic repulsion plays a dominant role in determining the relative energies of the possible JT distorted structures, but electron correlation effects are relatively unimportant.

Analysis of electron impact ionization properties of methane

“…The (1t 2 ) −1 ionic state, with electronic symmetry of 2 T 2 in the T d group, is unstable against Jahn‐Teller coupling. Ab initio calculations and experimental investigations have suggested a large distortion from the T d geometry to 12 equivalent C 2 v equilibrium structures [ Takeshita , 1987; Frey and Davidson , 1988; Boyd et al , 1991; Paddon‐Row et al , 1985; Knight et al , 1984; Vager et al , 1986]. The large Jahn‐Teller distortion has so far prevented the rotational structure of CH 4 + from being analyzed.…”

Symmetry breaking and structural distortions in chargedXH4(X=C,Si, Ge, Sn, and

“…Now it is generally agreed that the ground state structure of SiH 4 + has C s symmetry. Similarly, the structure of CH 4 + has been studied extensively [8,9,10,11,12,13,14,15,16], though there is still ambiguity regarding its ground state structure. The calculations done by the density functional theory( DFT ) methods show that the ground state structure of CH 4 + has D 2d symmetry [8,9],…”

The Protoadamantane Radical Cation

“…Even the qualitative results sensitively depend on the level of theory employed, especially for highly symmetrical hydrocarbons, which typically undergo JahnϪTeller distortions [22] (exceptions are known [23] ) upon ionization. For instance, the methane radical cation [24] is a C 2v -symmetrical minimum at MP2 and QCISD, but it is a transition structure at several DFT levels. [25] Nevertheless, computations are an indispensable tool for investigations of these species; recent high-level ab initio and DFT computations on radical cations derived from simple alkanes [21,25,26] tal structure is reported.…”