An investigation of valence shell orbital momentum profiles of difluoromethane by binary (e,2e) spectroscopy

Abstract

The electron binding energy spectra and momentum profiles of the valence orbitals of difluoromethane, also known as HFC32 (HFC-hydrofluorocarbon) (CH(2)F(2)), have been studied by using a high resolution (e,2e) electron momentum spectrometer, at an impact energy of 1200 eV plus the binding energy, and by using symmetric noncoplanar kinematics. The experimental momentum profiles of the outer valence orbitals and 4a(1) inner valence orbital are compared with the theoretical momentum distributions calculated using Hartree-Fock and density functional theory (DFT) methods with various basis sets. In general, the shapes of the experimental momentum distributions are well described by both the Hartree-Fock and DFT calculations when large and diffuse basis sets are used. However, the result also shows that it is hard to choose the different calculations for some orbitals, including the methods and the size of the basis sets employed. The pole strength of the ionization peak from the 4a(1) inner valence orbital is estimated.

Vibrational effects on valence electron momentum distributions of CH2F2

“…38,39 The present study supports their observation; it can be seen from Fig. 2 that the experimental result is in reasonable accordance with the equilibrium geometry calculation.…”

“…EMS studies. 28,38,39 It should be noted that the momentum space representation of a molecular orbital ϕ f (p;Q) is related to the corresponding position space wave function ϕ f (r;Q) by the Dirac-Fourier transform and thus its amplitude at p = 0 can be written as follows:…”

“…Indeed, for this molecule, a significant difference between experiment and theory has been reported for a valence orbital, 2b 1 , which has the CH-bonding character. 28,38,39 In the present work, electron momentum profiles of the valence orbitals of CH 2 F 2 have been measured experimentally with high statistical accuracy by using one of our multi-channel EMS spectrometer. 40 Theoretically, their electron momentum profiles have been calculated while effects of all the vibrational modes being involved.…”

Imaging Momentum Orbital Densities of Conformationally Versatile Molecules: A Benchmark Theoretical Study of the Molecular and Electronic Structures of Dimethoxymethane

“…Assuming that the usual symmetric non-coplanar geometric setup 1c is used for characterizing in coincidence the kinematics of (e,2e) ionization events, and that the binary encounter requirements of high impact energy, high momentum transfer, and negligible kinetic energy transfer to the residual ion are therefore fulfilled, the initial momentum p of the knocked-out electron can be monitored by scanning the azimuthal angle (φ) under which the electrons are selected, according to basic conservation laws on momenta and energies: and with E 1 ( p 1 ) and E 2 (p 2 ) the energies (momenta) of the two outgoing electrons, and where θ = θ 1 = θ 2 = 45° define the polar angles used in the experiment. In these equations, according to the characteristics of the experimental setup employed at Tsinghua University, the relevant parameters amount to p 1 = p 2 = 6.64077 au, p 0 = 0.271105 (1200 + E n ) 1/2 au (1 au = 1 a 0 -1 with a 0 the Bohr radius, i.e., 0.5292 Å), E Total = 1200 eV, and E 1 = E 2 = 600 eV. In this setup, the azimuthal angle φ varies from −38° to 38°, which enables measurements of (e,2e) ionization intensities up to electron momenta of ∼3.0 au.…”