Knowledge Bank

The BrCN$+$ ion was produced by Penning ionization of BrCN with metastable He$\ast$, and the near-infrared emission in the 690 - 870 nm region was measured by Fourier transform spectrometer. Thirteen vibronic bands of the $A~2\Sigma +-X~2\Pi$ transition of $\mathrm{<mrow\; data-mjx-texclass="ORD">79</mrow>}$BrCN$+$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">81</mrow>}$BrCN$+$ were observed. The rotational analysis was performed for the $A~2\Sigma +(000)-X~2\Pi \Omega (000)$ and $A~2\Sigma +(000)-X~2\Pi \Omega (010)$ transitions, both for the $\Omega =3/2$ and 1/2 spin components. \ Molecular constants, including the effective rotational constant, centrifugal distortion constant, $\Lambda$-type doubling constant in the $X~2\Pi 1/2$ state, and spin-rotation interaction constant in the $A~2\Sigma +$ state, were determined from the observed spectrum. Spin-orbit interaction constants for the $X~2\Pi$ ground state were determined to be $-$1476.4669(48) and $-$1476.4841(60)cm$^{-1}$, respectively, for $\mathrm{<mrow\; data-mjx-texclass="ORD">79</mrow>}$BrCN$+$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">81</mrow>}$BrCN$+$. The $r0$-structures for the $X~2\Pi$ and $A~2\Sigma +$ states of BrCN$+$ were derived to be compared with that for the $X~1\Sigma +$ 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 $X~2\Pi$(010) state was split into four components, $\mu 2\Sigma$, $\kappa 2\Sigma$, and $2\Delta P$ ($P=5/2$ and 3/2), and the rotational analysis was performed both for the $A~2\Sigma +-\mu 2\Sigma$ and $A~2\Sigma +-\kappa 2\Sigma$ transitions. For the $\mu 2\Sigma$ and $\kappa 2\Sigma$ vibronic states, $\Omega$-type doubling constants were determined as well as the rotational constants and centrifugal distortion constants. Renner parameter $ϵ$ for the $X~2\Pi$ state was determined to be $-0.185$ from the $\Omega$-type doubling constants for both the isotopic species.