We present results for the vibrational excitation of H 2 O by low-energy electrons (<10 eV). We calculate differential cross sections for the first excited states for all three modes using an R-matrix approach, at the static-exchange level, and the Chase approximation. Correction to the scattering amplitude for all partial waves (l > 3) is made using a closure approximation. The results are consistent with other theoretical treatments. For the bending mode there is agreement with two older experiments but disagreement with a more recent experiment at 7.5 eV. However, the present results for the stretch modes are less than the experimental values.
Electron energy loss spectra recorded at 135 • at constant scattered electron energies of 0.05, 0.6 and 3.0 eV, and with 10 meV resolution, reveal that the antisymmetric stretch vibration (001) is excited much less than the symmetric stretch vibration (100). Spectra subtraction indicates that the (001) level is excited about 5× less than (100) at 1 eV. Band profiles recorded 0.6 eV above threshold show that the J = 0 branch dominates the excitation of (010) and (100) vibrations but is absent for the (001) vibration. This indicates that resonant excitation is decisive for the (010) and (100) states but direct dipole mechanism for (001). The R-matrix adiabatic nuclei theory with closure approximation reproduces well the cross section for the (010) state, but dramatically underestimates the cross section for the symmetric stretch vibration and overestimates the cross section for the asymmetric stretch vibration.
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