Experimental Determination of theν5Cis-Bending Vibrational Frequency and Renner-Teller Structure in Ground State (X2Πu)C2H2+Using Laser Induced Reactions

The spectrum of the ${\nu }_5$ cis-bending vibration of ground state ($X^2{\Pi }_u$) ${\mathrm{C}}_2\mathrm{H}_2{}^{+}$ has been recorded applying the method of laser induced reactions in a low-temperature 22-pole ion trap. It is obtained by counting the number of products of the reaction ${\mathrm{C}}_2\mathrm{H}_2{}^{+}$ ($v_5=1$) $+{\mathrm{H}}_2\to {\mathrm{C}}_2\mathrm{H}_3{}^{+}+\mathrm{H}$ as a function of the laser wavelength. The vibronic transitions $\Delta \mathrm{\text{−}}\Pi$ and $\Sigma \mathrm{\text{−}}\Pi$ with their corresponding spin-orbit and Renner-Teller substructure have been observed. Using a perturbative analysis, the vibrational frequency has been determined to ${\omega }_5=(710\pm 4){\mathrm{c}\mathrm{m}}^{-1}$ and the Renner-Teller parameter ${ϵ}_5$ is on the order of $3\times {10}^{-2}$.