Total cross sections ($Q_T)$ for 1-500-eV positron and electron scattering by ${\mathrm{N}}_2$O are measured by a beam-transmission method. Comparisons of these results with prior electron and positron measurements of $Q_T$ for C${\mathrm{O}}_2$, ${\mathrm{N}}_2$, and CO, made by our group, reveal several remarkable similarities in the shapes and magnitudes of the $Q_T$ curves for the triatomic and also for the diatomic molecules. Small differences in the absolute $Q_T$ values for ${\mathrm{N}}_2$O and C${\mathrm{O}}_2$, and for ${\mathrm{N}}_2$ and CO, may be due to the weak permanent dipole moments of ${\mathrm{N}}_2$O and CO.

• Received 12 December 1983

DOI:https://doi.org/10.1103/PhysRevLett.52.1417