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 chorodifluoromethane(CHF2Cl)by binary(e,2e) electron momentum spectroscopy.The experimental data are compared with Hartree-Fock and density functional theory(DFT) calculations employing 6-31G,6-311 G^** and AUG-cc-pVQZ basis sets.For the summed momentum distribution of 8α′ 5α″ 7α′ 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 the basis set,but the improvement of the calculation quality is little in comparison with that calculated with the 6-311 G^** basis set,This indicates that the 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.     

Investigation of outer valence orbital of CF2Cl2 by a new type of electron momentum spectrometer

Electronic states of CF2Cl2 （dichlorodifluoromethane, Freon 12） have been studied using a new type of electron momentum spectrometer with a very high efficiency at an impact energy of 1200 eV plus binding energy. The experimental electron momentum profiles are compared with the density functional theory （DFT） and Hartree-Fock （HF） calculations. The relationship between orbital assignments in different coordinate systems is discussed. A new method of difference analysis based on the new type of electron momentum spectrometer is used to clarify the ambiguities regarding the orbital ordering.     

Electron momentum spectroscopy of NF3

The electronic structure of nitrogen trifluoride was investigated by combining the high-resolution electron momentum spectroscopy with the high-level calculations. The experimental binding energy spectra and the momentum distributions of each orbital were compared with the results of Hartree-Fock, density functional theory （DFT）, and symmetry-adapted- cluster configuration-interaction （SAC-CI） methods. SAC-CI and DFT-B3LYP with the aug-cc-pVTZ basis set can well reproduce the binding energy spectra and the observed momentum distributions of the valence orbitals except 1 a2 and 4e orbitals. It was found that the calculated momentum distributions using DFT-B3LYP are even better than those using the high-level SAC-CI method.     

A full-dimensional analytical potential energy surface for the F+CH_4→HF+CH_3 reaction

A full-dimensional analytical potential energy surface(APES) for the F + CH4 →HF + CH3 reaction is developed based on 7127 ab initio energy points at the unrestricted coupled-cluster with single,double,and perturbative triple excitations.The correlation-consistent polarized triple-split valence basis set is used.The APES is represented with a many-body expansion containing 239 parameters determined by the least square fitting method.The two-body terms of the APES are fitted by potential energy curves with multi-reference configuration interaction,which can describe the diatomic molecules(CH,H2,HF,and CF) accurately.It is found that the APES can reproduce the geometry and vibrational frequencies of the saddle point better than those available in the literature.The rate constants based on the present APES support the experimental results of Moore et al.[Int.J.Chem.Kin.26,813(1994)].The analytical first-order derivation of energy is also provided,making the present APES convenient and efficient for investigating the title reaction with quasiclassical trajectory calculations.     

Electronegativity explanation on the efficiency-enhancing mechanism of the hybrid inorganic–organic perovskite ABX_3 from first-principles study

Organic–inorganic hybrid perovskites play an important role in improving the efficiency of solid-state dye-sensitized solar cells. In this paper, we systematically explore the efficiency-enhancing mechanism of ABX_3(A = CH_3NH_3; B = Sn,Pb; X = Cl, Br, I) and provide the best absorber among ABX_3 when the organic framework A is CH_3NH_3 by first-principles calculations. The results reveal that the valence band maximum(VBM) of the ABX_3 is mainly composed of anion X p states and that conduction band minimum(CBM) of the ABX_3 is primarily composed of cation B p states. The bandgap of the ABX_3 decreases and the absorptive capacities of different wavelengths of light expand when reducing the size of the organic framework A, changing the B atom from Pb to Sn, and changing the X atom from Cl to Br to I. Finally, based on our calculations, it is discovered that CH_3NH_3 Sn I_3has the best optical properties and its light-adsorption range is the widest among all the ABX_3 compounds when A is CH_3NH_3. All these results indicate that the electronegativity difference between X and B plays a fundamental role in changing the energy gap and optical properties among ABX_3 compounds when A remains the same and that CH_3NH_3 Sn I_3 is a promising perovskite absorber in the high efficiency solar batteries among all the CH_3NH_3BX_3 compounds.     

Stability, defect and electronic properties of graphane-like carbon-halogen compounds

We perform first-principles total energy calculations to investigate the stabilities and the electronic structures of graphane-like structures of carbon-halogen compounds, where the hydrogen atoms in the graphane are substituted by halogen atoms. Three halogen elements, fluorine (F), chlorine (Cl) and bromine (Br), are considered, and the graphane-like structures are named as CF, CCl and CBr, respectively. It is found that for the single-atom adsorption, only the F adatom can be chemically adsorbed on the graphene. However, the stable graphane-like structures of CF, CCl and CBr can form due to the interaction between the halogen atoms. The carbon atoms in the stable CF, CCl and CBr compounds are in the sp³ hybridization, forming a hexagonal network similar to the graphane. The electronic band calculations show that CF and CCl are semiconductors with band gaps of 3.28 eV and 1.66 eV, respectively, while CBr is a metal. Moreover, the molecular dynamics simulation is employed to clarify the stabilities of CF and CCl. Those two compounds are stable at room temperature. A high temperature (≥1200 K) is needed to damage CF, while CCl is destroyed at 700 K. Furthermore, the effects of a vacancy on the structure and the electronic property of CF are discussed.     

Distorted Wave Effects of the 1b3g Orbital in Ethylene

We study the unexpected distorted wave effects of the 1b3g orbital in ethylene using a high resolution binary (e,2e) electron momentum spectrometer,at an impact energy of 800eV plus the binding energy (8-22eV) with symmetric non-coplanar kinematics.The experimental monentum profile of the 1b3g orbital is obtained and compared with the data previously measured at an impact energy of 1200 eV plus the binding energy.Also,the experimental momentum profiles of the 1b3g orbital are compared with the theoretical momentum distributions calculated by using Hartree-Fock and density functional theory methods.The experimental momentum profiles of the 1b3g orbital of ethylene at different impact energies show that the cross section of the orbital below the momentum p-1 a.u.is higher for lower impact energies.     

Experimental and calculated momentum densities for the complete valence orbitals of the antimicrobial agent diacetyl

The first electronic structural study of the complete valence shell binding energy spectra of the antimicrobial agent diacetyl, encompassing both the outer and inner valence regions, is reported. The binding energy spectra as well as the individual orbital momentum profiles have been measured by using a high resolution （e, 2e） electron momentum spectrometer （EMS） at an impact energy of 1200eV plus the binding energy, and using symmetric noncoplanar kinematics. The experimental orbital electron momentum profiles are compared with self-consistent field （SCF） theoretical profiles calculated using the Hartree-Fock approximation and Density Functional theory predictions in the target Kohn-Sham approximation which includes some treatment of correlation via the exchange and correlation potentials with a range of basis sets. The pole strengths of the main ionization peaks from the inner valence orbitals are estimated.     

The Utilization of Low Frequency Raman Spectra of Gases for the Study of Molecules with Large Amplitude Vibration

The utilization of the Raman spectra of the low frequency bending mode for three quasi-linear molecules: disiloxane,(SiH3)2O;methylisocyanate,CH3NCO;and dimethylisocyanate,(CH3)2SiHNCO for observing the low frequency anharmonic bending vibration is demonstrated which is superior to the corresponding far infrared spectra.From the observed frequencies from the Raman spectra the potential function governing the heavy atom motion to linearity has been obtained from which the barrier has been determined.These experimental values are compared to the ab initio predicted values.Also low frequency Raman spectra of the ring puckering vibration of chlorocyclobutane,c-C4H7Cl,bromocyclobutane,c-C4H7Br,and aminocyclobutane,c-C4H7NH2,have been utilized to obtain the potential function governing the ring inversion for these molecules.The determined barriers to planarity are compared to those obtained from MP2(full) ab initio and density functional theory B3LYP calculations by utilizing a variety of basis sets.For all of these studies it is shown that the Raman spectra are superior to the infrared spectra for determining the frequencies of the excited state transitions.