M. Roeselova et al., CYCLOBUTADIENE RADICAL-CATION - AN AB-INITIO STUDY OF THE JAHN-TELLERSURFACE, Chemical physics letters, 234(4-6), 1995, pp. 395-404
The Jahn-Teller potential energy surface of the cyclobutadiene radical
cation is reinvestigated at the CCSD(T)/TZP//RMP2/6-311G(2d, p) level
. It is found that out-of-plane deformations come into play as one mov
es away from the D-4h geometry. The relaxed radical cation has two pot
ential energy minima, a planar rectangle 1.7 kcal/mol below a puckered
rhombus, which are interconnected by a transition state lying 1.5 kca
l/mol above the latter. However, upon inclusion of zero-point energies
, the transition state falls 0.1 kcal/mol below the puckered minimum a
nd the enthalpies at 0 K of the three stationary points all lie within
0.54 kcal/mol. This indicates that the potential energy surface of th
is cation is strongly anharmonic. The repercussions of these findings
with regard to recent experiments are discussed.