Ultrahigh-resolution study of autodetachment inC2−

We describe a new coaxial laser-ion-beam photodetachment spectrometer designed to measure high-resolution photodetachment spectra of negative ions, and the measurement of ${\mathrm{C}}_2^{-}$ autodetachment rates with it. The apparatus resolution of 10 MHz is sufficient to resolve linewidth and line shape of autodetaching resonances in ${\mathrm{C}}_2^{-}$. Autodetachment rates of the $B{}_{}{}^2{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ state have been measured for a variety of rotational levels with $v^{\prime }=6, 7, 8, \mathrm{and} 9$. The observed rates vary between ${10}^7$ and ${10}^{10}$ ${\mathrm{s}}^{-1\mathrm{}}$, depending on vibrational and rotational state. Autodetachment of high vibrational levels ($v^{\prime }=19\mathrm{}$) of the $A{}_{}{}^2{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ state has been seen to be slower than ${10}^8$ ${\mathrm{s}}^{-1\mathrm{}}$. The physical processes giving rise to these results are discussed in some detail.