Electron Momentum Spectroscopy of the Frontier Orbitals of Chlorodifluoromethane

We report on the first measurement of the electron momentum distributions of the three outermost valence orbitals for chlorodifluoro-methane (CHF₂Cl) by a binary (e, 2e) electron momentum spectroscopy. The experimental data are compared with Hartree-Fock and density functional theory (DFT) calculations employing 6-31 G, 6-311++G^** and AUG-cc-pVQZ basis sets. For the summed momentum distribution of 8a'+5a''+7a' orbitals, the DFT/AUG-cc-pVQZ calculation gives the best fit. A very large and diffuse basis set, AUG-cc-pVQZ, is employed in the calculations to approach the Hartree-Fock limit of basis set, but improvement of the calculation quality is little in comparison with that calculated with 6-311++G^** basis set. This indicates that 6-311++G^** basis set is nearly saturated for the calculations of these three orbitals of CHF₂Cl, and it is unnecessary to employ a larger basis set in the calculations.