A new study of the perturbations in the A(1)Pi state of PN

The A(1) Pi-X(1) Sigma(+) system of the PN molecule has been reexamined via high resolution conventional spectroscopy, at higher rotational J-values than those in previous studies. It is shown that perturbations occurring in the A(1) Pi (upsilon = 0 to 3) levels give access to information concerning the (e(3) Sigma(-), a(3) Sigma(+), d(3) Delta, C-1 Sigma(-), D-1 Delta) valence states. Of particular interest are (1) the strong spin-orbit interaction between the e(3) Sigma(-) and A(1) Pi (upsilon(A) = 2) levels, yielding 17 rotational energy levels of the e(3) Sigma(-) state, and (2) the triple crossing occurring between the A(1) Pi (upsilon(A) = 3), d(3) Delta, and C-1 Sigma(-) levels. (C) 1996 Academic Press, Inc.