Large amplitude vibrations in the X [sup 2]A[sub 1] state of C[sub 2]B.

A three-dimensional potential energy function (PEF) of the [sup 2]A[sub 1] electronic ground state of C[sub 2]B has been generated by electronic structure calculations. The PEF possesses a minimum in an isosceles triangular structure which lies 2204 cm-1 below two equivalent minima having linear equilibrium geometry. The barrier height between the minima relative to the triangular structure has been calculated to the 2383 cm-1. The nuclear motion problem has been solved variationally in Jacobi coordinates for J=0 and 1. Ten vibrational states of A[sub 1] and nine of B[sub 2] symmetry are calculated to lie below the linear minima. The permutational splitting between the (000)[sup +] and (000)[sup -] states in the linear [sup 12]C[sub 2] [sup 11]B has been calculated to be 0.064 cm-1, in [sup 12]C[sup 13]C[sup 11]B this is 0.530 cm-1. Above the energy of the barrier to linearity there are large amplitude vibrations with triangular structure character. In the dense stack of such states vibrational modes of the linear structure are discernible, including their permutational splittings. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]