Measurements of valence orbital momentum profiles of n-butane by a high-resolution (e,2e) spectrometer

Assessment of Quantum Mechanical Models Based on Resolved Orbital Momentum Distributions of n-Butane in the Outer Valence Shell

“…In the outer valence shell, the orbital energies and their ordering often depend on the model employed due to the small orbital energy splitting. For example, ref gives the outer valence configuration for n -butane of C 2 h symmetry as (1a u ) 2 (5a g ) 2 (1b g ) 2 (5b u ) 2 (6b u ) 2 (6a g ) 2 (2a u ) 2 (2b g ) 2 (7a g ) 2 , whereas in ref , the configuration for the same species is (1a u ) 2 (5a g ) 2 (1b g ) 2 (5b u ) 2 (6b u ) 2 (2a u ) 2 (6a g ) 2 (2b g ) 2 (7a g ) 2 . The same group claimed that this configuration of the outer valence shell, based on HF/6-311G**, is (1a u ) 2 (5a g ) 2 (5b u ) 2 (1b g ) 2 (6b u ) 2 (2a u ) 2 (6a g ) 2 (2b g ) 2 (7a g ) 2 .…”

“…Nevertheless, the small orbital energy splitting in either n-butane 5 or isobutane 8,9 brings great challenges to the modern EMS technique and leads to partially resolved orbital momentum distributions, causing information loss in the chemically most significant region. Some recent EMS analysis, such as for n-butane, 3,4 employed high-level theoretical methods separately for the binding energies and orbital MDs. For example, the Green function calculations with various basis sets such as 1p-GF/ADC(3)/6-311G** 3 are used for the binding energies and B3LYP/6-311++G** 3 for the orbital cross section simulations of n-butane.…”

Orbital responses to methyl sites in CnH2n+2(n= 16)

“…We employ the B3LYP/TZVP//B3LYP/aug-cc-pVTZ method which has also been used in previous studies [49,50] for simulating orbital momentum distributions and geometry optimizations, and the simulation results are in excellent agreement with experimental data, which confirms that DFT can produce reliable results despite the dynamic instabilities in lower momentum space. [32] Detailed comparisons between experimental data and theoretical calculations for methane, [33,34,36] ethane, [35,39] propane, [38,41−43] n-butane, [37,45,47,49,51] and isobutane [40,44,48] can be found elsewhere, and the good agreement confirms that DFT is the best choice. Here, we only give the systematic trends of the orbital momentum distributions for C n H 2n+2 (n = 1-6) to obtain a more general conclusion.…”

“…[53] The selected SAOP model has been proven to be an effective way to describe ionization potentials (IPs) in the entire valence shell. [37] Molecular orbitals (MOs) obtained in coordinate space (based on the B3LYP/TZVP model) were directly mapped into momentum space as theoretical momentum distributions (TMDs). The Fourier transform and a number of approximations such as the Born-Oppenheimer approximation, the independent particle approximation, and the plane wave impulse approximation (PWIA), [54] were employed.…”

Electron Momentum Spectroscopy and Its Applications to Molecules of Biological Interest

“…Among the anisotropic property alternations, a particular group of molecular orbitals are responsible for certain conformations(Falzon and Wang, 2005). Although relatively simple, n-butane has small orbital energy splitting in the outer valence shell, which has brought challenges to the resolution of modem EMS experimental techniques.Consequently, the orbital momentum distributions are only partially resolved(Pang et al, 1998;Deng et al, 2001, Deng et al, 1999, leading to information loss in the chemically most significant region(Wang, 2003). Summaries of previous work on butane can be found in an incomplete list of al.…”