Ultrahigh-resolution study of autodetachment inC2−

Abstract

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