Ab initio molecular orbital study of the isomerization reaction surfaces of C3 and C3-

The potential-energy surfaces of C-3 and C-3(-) in the ground and some low-lying excited states are investigated by the CASSCF and MRD-CI methods to clarify the features of the isomerizations between the linear and bent structures. In addition, the asymmetric linear structures corresponding to the antisymmetric stretching mode in the (A) over tilde(1)Pi(u), state are examined. It is shown that the (a) over tilde(3)Pi(u), state of C-3 is isomerized into the equilateral triangle structure via an asymmetric transition state. Also, the central barrier height (215 cm(-1)) calculated for the double-minimum potential of (A) over tilde(1)Pi(u), agrees reasonably well with the experimental data (284.3 cm(-1)). (C) 1999 Elsevier Science B.V. All rights reserved.