15min:

YOSHIHIRO NAKASHIMA, TOMOKI OGAWA, MAKI MATSUO AND KEIICHI TANAKA, Department of Chemistry, Faculty of Science, Kyushu University 33, Hakozaki, Higashiku, Fukuoka 812-8581, Japan.

The BrCN⁺ ion was produced by Penning ionization of BrCN with metastable He^*, and the near-infrared emission in the 690 - 870 nm region was measured by Fourier transform spectrometer. Thirteen vibronic bands of the A^{2 +} - X² transition of ⁷⁹BrCN⁺ and ⁸¹BrCN⁺ were observed. The rotational analysis was performed for the A^{2 +}(000) - X² (000) and A^{2 +}(000) - X² (010) transitions, both for the =3/2 and 1/2 spin components.

Molecular constants, including the effective rotational constant, centrifugal distortion constant, -type doubling constant in the X² _1/2 state, and spin-rotation interaction constant in the A^{2 +} state, were determined from the observed spectrum. Spin-orbit interaction constants for the X² ground state were determined to be -1476.4669(48) and -1476.4841(60)~cm^-1, respectively, for ⁷⁹BrCN⁺ and ⁸¹BrCN⁺. The r₀-structures for the X² and A^{2 +} states of BrCN⁺ were derived to be compared with that for the X^{1 +} state of BrCN. The geometrical change of the BrCN⁺ ion from the BrCN molecule was turned out to be small.

Due to the Renner-Teller effect, the X² (010) state was split into four components, µ ² , ² , and ² _P (P=5/2 and 3/2), and the rotational analysis was performed both for the A^{2 +} - µ² and A^{2 +} - ² transitions. For the µ² and ² vibronic states, -type doubling constants were determined as well as the rotational constants and centrifugal distortion constants. Renner parameter for the X² state was determined to be -0.185 from the -type doubling constants for both the isotopic species.