Rotational Excitation of ${\mathrm{H}}_2\mathrm{O}$ by Cold Electrons

Experimental data are presented for the scattering of electrons by ${\mathrm{H}}_2\mathrm{O}$ between 17 and 250 meV impact energy. These results are used in conjunction with a generally applicable method, based on a quantum defect theory approach to electron-polar molecule collisions, to derive the first set of data for state-to-state rotationally inelastic scattering cross sections based on experimental values.

Figure 1

Integral (upper set) and backward cross sections (lower set) for scattering of electrons by ${\mathrm{H}}_2\mathrm{O}$ as a function of electron impact energy. Values are $\pm 5\%$. The solid lines are fits to theory (see text).

Figure 2

The form of the $\sigma$ (upper panel) and $\pi$ (lower panel) dipole harmonic waves for the dipole moment of water, 1.853 Debyes (0.729 a.u.).

Figure 3

Selected state-to-state integral cross sections for rotational excitation of the ${\mathrm{H}}_2\mathrm{O}$ molecule determined from experimental data. Full curves represent results for para-${\mathrm{H}}_2\mathrm{O}$ and dashed for ortho-${\mathrm{H}}_2\mathrm{O}$. The dotted curve represents elastic scattering for para-${\mathrm{H}}_2\mathrm{O}$ in its lowest rotational state. Curves with diamonds show the results of $R$-matrix calculations in Ref. 12.