We have measured the (c) over tilde-(X) over tilde laser excitation spectra of the Hg-N-2 and CO collisional quasimolecules for the formation of Hg(6(3)P(2)) and Hg(6(3)P(1)) in the far wings of the Hg 6(1)S(0)-6(3)P(2) dipole-forbidden line. These are the first observations of the (c) over tilde-(X) over tilde bands in Hg-molecule systems. It is found that Hg(6(3)P(1)) is efficiently produced via a nonadiabatic transition from the (c) over tilde state. This is in striking contrast with the Hg-rare gas cases where no nonadiabatic processes have been observed. (C) 1999 Elsevier Science B.V. All rights reserved.