15min:

TAKASHI IMAJO, KEN TOKIEDA, KEIICHI TANAKA AND TAKEHIKO TANAKA, Department of Chemistry, Faculty of Science, Kyushu University 33, Hakozaki, Higashi ku, Fukuoka 812-8581, Japan..

High resolution Fourier transform emission spectrum of the B ²⁺ - X ²⁺ band of the PN⁺ ion was observed in the ultra violet region around 31000~cm^-1 with Bruker IFS120HR. The rotationally resolved spectrum of PN⁺, produced by an ac discharge of the PCl₃, N₂, and He gas mixture, was recorded for about 11~h accumulating the interferogram 1600 times. The monochromator placed just before a photomultiplier worked effectively as an optical filter with a band width of 200~cm^-1. The (0,0) band lines split into doublet due to the spin-rotation splitting were assigned to the R- and P- branch lines of N'' up to 35. The determined band origin ₀=31058.9963(81) cm^-1 is consistent with the previous low resolution result [1]. The rotational, centrifugal distortion constants for both states were determined as well as the spin-rotation constant for the ground state. The B ²⁺ state has weaker bond than that of the ground state, since the bond length of the B ²⁺ (v=0) state (1.570~Å) is by 0.076~Å~longer, and the force constant ( k = 2.90 mdyne/Å) is by about 70~% smaller than those of the ground state. Present results support the ab initio calculation which predicts a shallow minimum for the B ²⁺ state due to avoided crossing [2].

\noindent 1. I. K. Ahmad and P. A. Hamilton, J. Mol. Spectrosc., 163, 214 (1994).
\noindent 2. F. Grein, Chem. Phys. Lett., 120, 383 (1988).\bigskip