The ab initio calculation of photoelectron angular distributions (PADs) for anions remains a theoretical challenge. In this work we report a joint experimental and theoretical investigation of PADs for nonpolar ${\mathrm{O}}_2{}^{-}$, weakly polar $\mathrm{N}{\mathrm{O}}^{-}$, and strongly polar $\mathrm{As}{\mathrm{O}}^{-}$ and $\mathrm{Sb}{\mathrm{O}}^{-}$. We also determine the electron affinities of AsO and SbO to be 10 318(7) and $12426\left(7\right)\mathrm{c}{\mathrm{m}}^{-1}$, respectively. To improve the description of the long-range region of the initial-state wave function, which contributes strongly to the photodetachment transition amplitude, we modified the standard Gaussian-type orbitals by augmenting them with a correct exponential Slater-tail basis set (approximately $e^{-\xi r}$). This simple yet effective approach substantially improves the agreement between experiment and calculation for ${\mathrm{O}}_2{}^{-}$ and for most vibrational channels of $\mathrm{N}{\mathrm{O}}^{-}$. However, notable discrepancies persist for $\mathrm{N}{\mathrm{O}}^{-}$ for transitions to the $v=0$ vibrational level of neutral NO even after this correction. Given that our methodology successfully reproduces PADs for strongly polar anions, e.g., $\mathrm{As}{\mathrm{O}}^{-}$ and $\mathrm{Sb}{\mathrm{O}}^{-}$, these residual discrepancies are unlikely to stem from exit-channel scattering induced by long-range dipole fields. Instead, we tentatively attribute the remaining discrepancy for $\mathrm{N}{\mathrm{O}}^{-}$ to the breakdown of the Born-Oppenheimer approximation or the frozen-orbital approximation, arising from the extremely weak binding of the excess electron.

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• Long-range interactions
• Photodetachment
• Photoelectron techniques