Knowledge Bank

The $OCS+$ ion was produced by Penning ionization of OCS with metastable $He\ast$, and UV emission in the 370 --- 500 nm region was measured by Fourier transform spectrometer. The $A~2\Pi -X~2\Pi$ electronic transition has been reported in the 300 --- 500 nm region, but only the emission bands from the vibrational ground state of the $A~\Pi 2$ state were observed because of the predissociation in the $A~2\Pi$ $statea$. High resolution study of the 0-0 band has been reported for both the $\Omega =3/2$ and $\Omega =1/2$ spin $statesb,c$. In the present study, seven rotationally resolved bands were observed in the 370 --- 500 nm region and assigned to the CO stretch $(\nu 3\prime \prime )$ progression: $A~2\Pi 3/2(000)-X~2\Pi 3/2(00v)(v=2-5)$ and $A~2\Pi 1/2(000)-X~2\Pi 1/2(00v)(v=3-4)$. The observed lines of the $\Omega =1/2$ substate were split into the two components due to the A-type doubling. The spectra for $\Omega =3/2$ and $\Omega =1/2$ were analysed separately to obtain molecular constants for each spin state. Band origins, vibrational frequencies, rotational constants, vibrational-rotational constants for both spin substates and A-type doubling constant for the $\Omega =1/2$ substate were determined by a least squares fitting. Rotational constants in the vibrational ground state were determined for both spin states. The spin-orbit interaction constants derived from these rotational constants, $A\prime =-125.0cm-1$ and $A\prime \prime =-383.8cm-1$, are consistent with those derived from the photodissociation $studyd$.