LASER SPECTROSCOPY OF CCH IN THE $36600-39700 cm^{-1}$ REGION

$^{a}$Y.-C. Hsu, J. J.-M. Lin, D. Papou$\bar{s}$ek, and J.-J. Tsai, J.Chem. Phys. 98, 6690(1993). $^{b}$ Y.-C. Hsu, Y.-J. Shiu, and C.-M. Lin, J. Chem. Phys. 103, 5919(1995).Author Institution: Institute of Atomic and Molecular Sciences; Department of ChemistryIn the $36600-39700 cm^{-1}$ range, eight new bands of CCH $B^{2}A^{\prime}\leftarrow \tilde{X}^{2}\Sigma$ transition were observed by laser-induced fluorescence. By rotational analysis, they have been assigned as transitions from low vibronic levels, $\tilde{X}(0, v_{2}, v_{3}) (v_{2}=2-4$ and $v_{3}=0-1$) of CCH to two vibrational levels (T, T+1221) of the $\tilde{B}$ state. Most of these bands were difficult to be detected if a acetylene/argon or helium gas mixture was photolyzed to produce CCH. Due to population transfer, via collisions with $SF_{6}$, from higher vibronic levels of CCH which were predominantly produced in the 193.3 nm photolysis of acetylene, spectral intensities of these bands were thus enhanced. Spectroscopic parameters of $\tilde{X}(0,2^{0}, 0),\tilde{X}(0,2^{2}, 0),\tilde{X}(0,2^{2},1) $ and $\tilde{B}(T+1221)$ were obtained for the first time. Spectral lines of transition $\tilde{B}(T)\leftarrow\tilde{X}(0, 3^{0,3}, 0)$ recorded in a supersonic beam were also included in a simultaneous fit, spectroscopic parameters of $\tilde{X}(0, 3^{0,3},0)$ were accordingly better determined in this work than our previous $reports.^{a,b}$ The vibronic energy levels $\tilde{X}(0, v_{2}, v_{3})(v_{3}=0-2)$ of CCH up to $5500 cm^{-1}$ were approximated as three anharmonic oscillators, where $v_{2}$ is 401 cm. The anharmonicities and 911#### obtained from the fit will be given