Knowledge Bank

We have recently observed two vibrational hot bands from the $\Pi (010)$ of the ground electronic state of the $CCH(x2\Sigma +)$ radical by using IR diode laser kinetic spectroscopy. One band was observed in $1720cm-1$ region and was assigned to the $\pi (011)-\pi (010)$ transition. Combined with a previous result on the $\pi (011)-\pi (000)band1$), the $\nu 2$ fundamental frequency was determined for the first time to be $370.1537(15)cm-1$. This value is in good agreement with an estimate using the 1-type doubling $constant2$). The other band was observed in $1790cm-1$ region and the upper state is tentatively assigned to the $\pi (0710)$ state from the $\nu 2$ frequency above mentioned. The vibrational term values, other molecular constants, and the intensity of spectra suggest that the $A\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ state perturbs strongly vibrational states of the ground electronic state.