Ab Initio Molecular Orbital Theory Research Articles

Computational study on the bifurcation mechanism in the H2CO− + CH3Cl →CH3CH2O + Cl−/H2CO + CH3 + Cl− reaction: The importance of intramolecular vibrational redistributions

We have investigated the bifurcation dynamics of the H2CO− + CH3Cl →CH3CH2O + Cl− (C-substitution channel)/H2CO + CH3 + Cl− (electron transfer channel) reaction using three different molecular dynamics (MD) methods: quasi-classical trajectory (QCT), classical MD, and ring-polymer MD simulations. All MD calculations were performed using the on-the-fly approach at the ab initio molecular orbital theory level. We found that the C-substitution channel is dominant in the classical and ring-polymer MD calculations, while the electron transfer channel is dominant in the QCT calculations. The different bifurcation mechanisms in the types of MD simulations were investigated using supervised machine-learning classification. This difference is attributed to the varying efficiency of the intramolecular vibrational redistribution process among the different MD methods. Thus, in the bifurcation mechanism of the H2CO− + CH3Cl reaction, the bifurcation fractions are primarily determined by the vibrational dynamics occurring in the later stages of the reaction.

Chemical significance of x-ray photoelectron spectroscopy binding energy shifts: A Perspective

The principal intent of this Perspective is to review the mechanisms that are responsible for the shifts of binding energies, ΔBE, observed in x-ray photoelectron spectroscopy (XPS) measurements and so to relate the shifts to the electronic structure and the chemical bonding in the systems studied. To achieve this goal, several theoretical considerations are necessary beyond just the calculation of XPS BEs. Though briefly discussed here, we are not primarily interested in absolute values of BE or quantitation using relative intensities. Within the molecular orbital (MO) theory framework, it is shown that the analysis of orbital properties is critical for the correct interpretation of XPS. In particular, rigorous definitions are given for the initial state and final state contributions to BEs and to BE shifts, ΔBE. It is first shown how the BEs of core levels are related to the electronic structure by consideration of the BEs for a model atomic system to establish the origins and magnitudes of BE shifts. The mechanisms established for the model system are then applied to a review of XPS measurements and MO theory on a set of real examples. An important focus of the paper is to demonstrate that, in many cases, initial state mechanisms allow for a definitive interpretation of the XPS BE shifts and that an important role of theory is to provide qualitative explanations rather than quantitative agreement with XPS measurements. The mechanisms established are a guide to the interpretation of XPS measurements and consideration of these mechanisms may suggest additional calculations that would be useful. It is concluded that there is still a bright future for the coupling of ab initio MO theory with XPS measurements.

Theoretical Study on Mechanism for the Reaction of 2-propargyl radical (C3H3) with ammonia (NH3)

A theoretical study of the mechanism and kinetics of the reaction of 2-propargyl radical, H2CCCH, with ammonia, NH3, has been carried out by ab initio molecular orbital theory based on CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++(3df,2p) method. The potential energy surface (PES) for the C3H3 + NH3 reaction was established, showing that the reaction has four principal entrance channels. Two H-abstraction reactions from NH3, leading to propyne or allene + NH2. The addition reactions start by formation of two intermediates H2CCCHNH3 and H2CC(NH3)CH. From these two intermediate states, many other transition states and intermediate states can be accessed, leading to 21 possible products. The reaction has sizable entrance energy barriers, though the H-abstraction entrance channels might contribute significantly at high temperatures, where formation of HCCCH3 + NH2 is more energetically favorable.

Investigation of the Correlation between Geometrical Relationship and the Anomeric effect on Conformational Reactivities and Analyze the 1, 4-elimination

Abstract: Ab initio molecular orbital hybrid density functional theory (B3LYP/6-311++G**) based methods and natural bond orbital (NBO) interpretation were used to investigate the 1, 4- eliminations and the correlations between the global hardness, global electronegativity, anomeric effect, thermodynamic parameters of 3-chloro-8-methyl-8- azabicyclo[3.2.1]octane (1), 3-chloro-8-methyl-8- phosphabicyclo[3.2.1]octane (2) and 3-chloro-8-methyl-8- arsabicyclo [3.2.1]octane (3). The calculated global electronegativity (χ) differences between the axial- and equatorial-stereoisomers (Δ [χ (eq) - χ (ax)]) decreased from compound 1 to compound 3. This fact justifies that with the increase of the Lewis acid from the equatorial- stereoisomers of compound 1 to compound 3, the energy difference between the axial- and equatorial- stereoisomers decreases. NBO results showed that the anomeric effect is in benefit of the equatorial stereoisomers. The reactions shown in this work are illustrative of the power of anomeric effect and the geometrical relationship of the participating bonds. If the rC-Cl bond is axial, the 1, 4-elimination is avoided altogether. Whereas, if the rC-Cl bond is equatorial, the 1, 4-elimination is performed. These eliminations are rendered possible by the antiperiplanar relationship of the breaking central rC–C bond with the electron pair orbital on the heteroatom and the rC–X bond, X being a leaving group such as a halogen.

An ab initio study of the structural, vibrational and electronic properties of some tetrel-bonded complexes of methane and tetrafluoromethane

The binary complexes of ammonia, water, hydrogen fluoride, phosphine, hydrogen sulphide and hydrogen chloride, as electron donors, with methane and tetrafluoromethane, as electron acceptors, have been studied by means of ab initio molecular orbital theory. The properties of interest are the molecular structures, interaction energies and vibrational spectra of the complexes, and the interactions of the molecular orbitals which result in the formation of the complexes. The adducts were found to fall into a number of structural types, including tetrel-bonded, hydrogen-bonded, halogen-bonded, pnicogen-bonded and chalcogen-bonded, depending on the particular combination of electron donor and acceptor. The complexes, irrespective of the type of interaction, were found to be uniformly very weakly bound. The results have been rationalized in terms of the properties of the donors and, together with the conclusions of previous studies involving methyl fluoride, difluoromethane and fluoroform, with the extent of fluorine substitution in the parent molecule, methane.

Structural, vibrational and electronic properties of some tetrel-bonded complexes of the fluorinated methanes methyl fluoride, difluoromethane and fluoroform: an ab initio study.

A search has been conducted, by means of ab initio molecular orbital theory, for potential tetrel-bonded complexes formed between the fluorinated methanes methyl fluoride, difluoromethane and fluoroform, and the related hydrides ammonia, water, hydrogen fluoride, phosphine, hydrogen sulphide and hydrogen chloride. Eleven such complexes have been identified, six containing CH3F and five CH2F2. The complexes are typically less strongly bound than their hydrogen-bonded counterparts, and the interaction energies vary in a consistent way with the periodic trend of the electron donors. The intermolecular separations and changes of the relevant intramolecular bond lengths, the wavenumber shifts of the critical vibrational modes and the extents of charge transfer correlate, by and large, with the strengths of interaction.

From six to eight Π-electron bare rings of group-XIV elements and beyond: can planarity be deciphered from the "quasi-molecules" they embed?

Ab initio molecular orbital theory is used to study the structures of six and eight π-electron bare rings of group-XIV elements, and even larger [n]annulenes up to C18H18, including some of their mono-, di-, tri-, and tetra-anions. While some of the above rings are planar, others are nonplanar. A much spotlighted case is cyclo-octatetraene (C8H8), which is predicted to be nonplanar together with its heavier group-XIV analogues Si8H8 and Ge8H8, with the solely planar members of its family having the stoichiometric formulas C4Si4H8 and C4Ge4H8. A similar situation arises with the six π-electron bare rings, where benzene and substituted ones up to C3Si3H6 or so are planar, while others are not. However, the explanations encountered in the literature find support in ab initio calculations for such species, often rationalized from distinct calculated features. Using second-order Møller-Plesset perturbation theory and, when affordable (particularly tetratomics, which may allow even higher levels), the coupled-cluster method including single, double, and perturbative triple excitations, a common rationale is suggested based on a novel concept of quasi-molecules or the (3+4)-atom partition scheme. Any criticism of tautology is therefore avoided. The same analysis has also been successfully applied to even larger [n]annulenes, to their mixed family members involving silicon and germanium atoms, and to the C18 carbon ring. Furthermore, it has been extended to annulene anions to check the criteria of the popular Hückel rule for planarity and aromaticity. Exploratory work on cycloarenes is also reported. Besides a partial study of the involved potential energy surfaces, equilibrium geometries and harmonic vibrational frequencies have been calculated anew, for both the parent and the actual prototypes of the quasi-molecules.

Hydrogen and Halogen Bonding in Homogeneous External Electric Fields: Modulating the Bond Strengths.

Recent years have witnessed various fascinating phenomena arising from the interactions of noncovalent bonds with homogeneous external electric fields (EEFs). Here we performed a computational study to interpret the sensitivity of intrinsic bond strengths to EEFs in terms of steric effect and orbital interactions. The block-localized wavefunction (BLW) method, which combines the advantages of both ab initio valence bond (VB) theory and molecular orbital (MO) theory, and the subsequent energy decomposition (BLW-ED) approach were adopted. The sensitivity was monitored and analyzed using the induced energy term, which is the variation in each energy component along the EEF strength. Systems with single or multiple hydrogen (H) or halogen (X) bond(s) were also examined. It was found that the X-bond strength change to EEFs mainly stems from the covalency change, while generally the steric effect rules the response of H-bonds to EEFs. Furthermore, X-bonds are more sensitive to EEFs, with the key difference between H- and X-bonds lying in the charge transfer interaction. Since phenylboronic acid has been experimentally used as a smart linker in EEFs, switchable sensitivity was scrutinized with the example of the phenylboronic acid dimer, which exhibits two conformations with either antiparallel or parallel H-bonds, thereby, opposite or consistent responses to EEFs. Among the studied systems, the quadruple X-bonds in molecular capsules exhibit remarkable sensitivity, with its interaction energy increased by -95.2 kJ mol-1 at the EEF strength 0.005 a.u.

Computational Investigation on the Formation and Decomposition Reactions of the C4H3O Compound.

Gas-phase mechanism and kinetics of the formation and decomposition reactions of the C4H3O compound, a crucial intermediate of the atmospheric and combustion chemistry, were investigated using ab initio molecular orbital theory and the very expensive coupled-cluster CCSD(T)/CBS(T,Q,5)//B3LYP/6-311++G(3df,2p) method together with transition state theory and Rice–Ramsperger–Kassel–Macus kinetic predictions. The potential energy surface established shows that the C3H3 + CO addition reaction has four main entrances in which C3H3 + CO → IS1-cis (CHCCH2CO) is the most energetically favorable channel. The calculated results revealed that the bimolecular rate constants are positively dependent on both temperatures (T = 300–2000 K) and pressures (P = 1–76,000 Torr). Of these values, the k1 rate constant of the C3H3 + CO → IS1-cis addition channel is dominant over the 300–2000 K temperature range, increasing from 1.53 × 10–20 to 1.04 × 10–13 cm3 molecule–1 s–1 with the branching ratio reducing from 62% to 44%. The predicted unimolecular rate coefficients in the ranges of T = 300–2000 K and P = 1–76,000 Torr revealed that the intermediate products IS1-cis, IS1-trans, and IS2 are rather unstable and would rapidly decompose back to the reactants (C3H3 + CO), especially at high temperatures (T > 1000 K). The high-pressure limit rate constants for the C4H3O decomposition leading to products (C3H3 + CO), (CHCCHCO + H), and (CHCO + C2H2) have been found to be in excellent agreement with the available literature values proposed by Tian et al. (Combust. Flame, 2011,158, 756–773) without any adjustment from the ab initio calculations. Therefore, the predicted temperature- and pressure-dependent rate constants can be confidently used for modeling CO-related systems under atmospheric and combustion conditions.

Theoretical insight into the mechanisms of the gas-phase decomposition of azidoacetone

A theoretical study of the mechanisms for the gas-phase decomposition of azidoacetone was performed using ab initio molecular orbital theory based on the QCISD(T)/aug-cc-pVTZ//MP2(full)/6–311++G(d,p) + 0.95 × ZPE method. The calculated results clearly show that the imine CH3C(O)N = CH2 formed through Curtius rearrangement route in conjunction with the cyclic amine and the imine CH3(CO)CH = NH play a crucial role in the gas-phase decomposition of azidoacetone. The fragmentation and/or isomerization these three intermediates giving rise to CH2CO, CH2 = NH, CO, CH3N = CH2, CH3CHO and HCN becomes the key reaction pathways. Our calculated results are in excellent consistent with the experimental findings.

Kinetics and mechanisms of OH-induced 2-ethoxyethanol oxidation in the atmosphere

The mechanisms and kinetics for the reaction of 2-ethoxyethanol (2EE) with OH radicals in the presence of O2/NO were carried out using ab initio molecular orbital theory based on the QCISD(T)/6-311++G(d,p)//BH&HLYP/6-311++G(d,p) method in conjunction with transition state theory (TST) coupled with Wigner’s tunneling correction at temperatures between 200 and 1000 K. The calculated results indicate that ethylene glycol monoacetate [CH3C(O)OCH2CH2OH], ethylene glycol monoformate [HC(O)OCH2CH2OH], formaldehyde [HC(O)H], ethyl glycolate [CH3CH2OC(O)CH2OH], and ethyl formate [CH3CH2OC(O)H] can be the major products for the reaction of 2EE + OH in the presence of O2/NO, which are in excellent accord with the experimental observations. The rate constant for the reaction of OH radicals with 2EE at 298 K is computed to be 3.14 × 10−11 cm3 molecule−1 s−1, which is in stronger agreement with the experimental value given by Colmenar et al. (2.17 ± 0.11) × 10−11 cm3 molecule−1 s−1. In the temperature range of 200−1000 K, the calculated TST rate constants for the OH+2EE reaction can be expressed as a function of temperature with k = 1.15 × 10−14 × (T/298)3.9 × exp (2338.2/T) cm3 molecule−1 s−1.

Theoretical Investigation of the Mechanisms and Kinetics of the Bimolecular and Unimolecular Reactions Involving in the C4H6 Species

A theoretical study of the mechanisms and kinetics for the C4H6 system was carried out using ab initio molecular orbital theory based on the CCSD(T)/CBS//B3LYP/6-311++G(3df,2p) method in conjunction with statistical theoretical variable reaction coordinate transition-state theory and RRKM/ME calculations. The calculated results indicate that buta-1,3-diene, but-1-yne, and C4H5 + H can be the major products of the C3 + C1 reaction, while CCH2 + C2H4 and C4H5 + H play an important role in the C2 + C2 reaction. In contrast, the C4H6 fragmentation giving rise to C3 + C1 and C4H5 + H becomes the key reaction paths under any temperature and pressure. The rate constants for the system have been calculated in the 300-2000 K temperature range at various pressures for which the C2 + C2 → C4H6 high-P limit rate constant, 10.24 × 1014T-0.51 cm3/mol/s, agrees well with the measured value of Hidaka et al., 9.64 × 1014T-0.5 cm3/mol/s. Also, the high-P limit rate constants of the channels but-2-yne → 2-C4H5 + H and C3 + C1 → C4H6, being 1.7 × 1014 exp(-351.5 kJ·mol-1/RT) s-1 and 5.07 × 1013 exp(0.694 kJ·mol-1/RT) cm3/mol/s, are in good agreement with the available literature data 5 × 1014 exp(-365.3 kJ·mol-1/RT) s-1 and 4.09 × 1013 exp(1.08 kJ·mol-1/RT) cm3/mol/s reported by Hidaka et al. and Knyazev and Slagle, respectively. Moreover, the 298 K/50 Torr branching ratios for the formation of buta-1,2-diene (0.43) and but-1-yne (0.57) as well as the total rate constant 5.18 × 1013 cm3/mol/s of the channels C3 + C1 → buta-1,2-diene and C3 + C1 → but-1-yne are in excellent accord with the laboratory values given by Fahr and Nayak, being 0.4, 0.6, and (9.03 ± 1.8) × 1013 cm3/mol/s, respectively. Last but not least, the rate constants and branching ratios for the C4H6 dissociation processes in the present study also agree closely with the theoretically and experimentally reported data.

A Theoretical Study of Hydrogen-Bonded Complexes of Ethylene Glycol, Thioglycol and Dithioglycol with Water

In the present study, a theoretical analysis of hydrogen bond formation of ethylene glycol, thioglycol, dithioglycol with single water molecule has been performed based on structural parameters of optimized geometries, interaction energies, deformation energies, orbital analysis and charge transfer. ab initio molecular orbital theory (MP2) method in conjunction with 6-31+G* basis set has been employed. Twelve aggregates of the selected molecules with water have been optimized at MP2/6-31+G* level and analyzed for intramolecular and intermolecular hydrogen bond interactions. The evaluated interaction energies suggest aggregates have hydrogen bonds of weak to moderate strength. Although the aggregates are primarily stabilized by conventional hydrogen bond donors and acceptors, yet C-H···O, S-H···O, O-H···S, etc. untraditional hydrogen bonds also contribute to stabilize many aggregates. The hydrogen bonding involving sulfur in the aggregates of thioglycol and dithioglycol is disfavoured electrostatically but favoured by charge transfer. Natural bond orbital (NBO) analysis has been employed to understand the role of electron delocalizations, bond polarizations, charge transfer, etc. as contributors to stabilization energy.

Molecular Design of Aromatic Polythionoesters

As an example of molecular design of new polymers, structures and properties of poly(ethylene thionoterephthalate) (PET[S2]) and the related polymers have been predicted from calculations of ab initio molecular orbital (MO) theory, rotational isomeric state (RIS) scheme, and periodic density functional theory (DFT). The MO calculations were confirmed by NMR experiments and introduced to the RIS scheme for PET[S2] to yield its configurational properties, which are compared herein with those of analogous polyester, polythioester, and polydithioester. Configurational properties of randomly thiono-substituted poly(ethylene terephthalate) (PET), PET[SzO1–z], were also evaluated as a function of sulfidity (z). On the assumption that the crystal of PET[S2] can be expressed as an isomorphic replacement of the PET crystal, the crystal structure was optimized by a periodic DFT simulation and its Young’s moduli in the a-, b-, and c-axis directions were, respectively, evaluated to be Ea = 0.94(7.20) GPa, Eb = 19.58(22.26) GPa, and Ec = 142.1(182.4) GPa, where the parenthetic values are those of the PET crystal. There is a possibility that properties of PET[SzO1–z] will be controlled between those of PET and PET[S2] by adjusting the sulfidity. The potential practical applications of the polythionoesters are also discussed herein. By purely theoretical computations, the structures and properties of the not-yet synthesized polymers were predicted quantitatively; that is, the theoretical molecular design of new polymers has been achieved.

Mechanism and kinetics of the reaction of the 2‐propargyl radical with ammonia

AbstractGas‐phase mechanism and kinetics of the reactions of the 2‐propargyl radical (H2CCCH), an important intermediate in combustion processes, with ammonia were investigated using ab initio molecular orbital theory at the coupled‐cluster CCSD(T)//B3LYP/6‐311++G(3df,2p) method in conjunction with transition state theory (TST), variational transition state theory (VTST), and Rice–Ramsperger–Kassel–Macus (RRKM) calculations for rate constants. The potential energy surface (PES) constructed shows that the C3H3 + NH3 reaction has four main entrances, including two H‐abstraction and two addition channels in which the former are energetically more favorable. The H‐abstraction channels occur via energy barriers of 24 (T0/P2) and 26 kcal/mol (T0/P3) forming loose van de Waals complexes, COM_1 (12 kcal/mol) and COM_2 (14 kcal/mol), respectively. These complexes can easily be decomposed via barrier‐less processes resulting HCCCH3 + NH2 (P2, 14 kcal/mol) and HCCCH3 + NH2 (P3, 15 kcal/mol), respectively. The additional channels occur initially by formation of two intermediate states, H2CCCHNH3 (35 kcal/mol) and H2CC(NH3)CH (37 kcal/mol) via energy barriers of 37 and 40 kcal/mol at T0/1 and T0/5, respectively, followed by isomerization and decomposition yielding 21 different products. These processes are fully depicted in an as‐complete‐as‐possible PES. The rate constants and product branching ratios for the low‐energy channels calculated show that the C3H3 + NH3 reaction is almost pressure‐independent. For the temperature range of 300–2000 K, the HCCCH3 + NH2 is the major product, whereas the minor one, HCCCH3 + NH2, has more contribution when temperature increases. Theoretical results on the mechanism and kinetics of the reaction considered may be helpful for future experiments as well as for understanding the role of the propargyl radical in combustion chemistry.

Theoretical Investigation on Mechanism, Thermochemistry, and Kinetics of the Gas-phase Reaction of 2-Propargyl Radical with Formaldehyde

Gas-phase mechanism and kinetics of the reactions of the 2-propargyl radical(H2CCCH), an important intermediate in combustion processes, with formaldehyde were investigated using ab initio molecular orbital theory at the coupled-cluster CCSD(T)//B3LYP/6-311++G(3df, 2p) method in conjunction with transition state theory(TST), variational transition state theory(VTST) and Rice-Ramsperger-Kassel-Marcus(RRKM) calculations for rate constants. The potential energy surface(PES) constructed shows that the H2CCCH+HCHO reaction has six main entrances, including two H-abstraction and four additional channels, in which the former is energetically more favorable. The H-abstraction channels slide down to two quite weak pre-complexes COM-01(−9.3 kJ/mol) and COM-02(−8.1 kJ/mol) before going via energy barriers of 71.3(T0/P1) and 63.9 kJ/mol(T0/P2), respectively. Two post-complexes, COM-1(−17.8 kJ/mol) and COM-2(−23.4 kJ/mol) created just after coming out from T0/P1 and T0/P2, respectively, can easily be decomposed via barrier-less processes yielding H2CCCH2+CHO(P1, −12.4 kJ/mol) and HCCCH3+CHO(P2, −16.5 kJ/mol), respectively. The additional channels occur initially by formation of four intermediate states, H2CCCHCH2O(I1, 1.1 kJ/mol), HCCCH2CH2O(I3, 4.5 kJ/mol), H2CCCHOCH2(I4, 10.2 kJ/mol), and HCCCH2OCH2(I6, 19.1 kJ/mol) via energy barriers of 66.3, 59.2, 112.2, and 98.6 kJ/mol at T0/1, T0/3, T0/4, and T0/6, respectively. Of which two channels producing I4 and I6 can be ignored due to coming over the high barriers T0/4 and T0/6, respectively. The rate constants and product branching ratios for the low-energy channels calculated show that the H2CCCH+HCHO reaction is almost pressure-independent. Although the H2CCCH+HCHO→I1 and H2CCCH+HCHO→I3 channels become dominant at low temperature, however, they are less competitive channels at high temperature.

Ab initio chemical kinetics for hypergolic reactions of nitrogen tetroxide with hydrazine and methyl hydrazine

The kinetics and mechanisms for the hypergolic reactions of N2O4 (NTO) with N2H4 and CH3NHNH2 have been investigated by ab initio molecular orbital theory based on the UCCSD(T) method with the 6-311+G(3df, 2p) basis set. These reactions are important to the propulsion chemistry of the N2O4-N2H3X (X = H, CH3) propellant systems. The results of our calculations show that the hypergolic ignition reactions of NTO with N2H4 and CH3NHNH2, producing N2H3NO + HNO3 and CH3NHN(H)NO/CH3N(NO)NH2 + HNO3, respectively, can be initiated by the rapid attack of hydrazine molecules by ONONO2, following the isomerization of NTO via loose, roaming-like transition states with 5.9 and 6.3 kcal/mol above the reactants in the presence of the hydrazine reactants as spectators. The rate constants for the reactions have been predicted in the temperature range 298–2000 K with the transition state theory; the result indicates, for example, that the half-life of N2O4 at 300 K in a mixture containing an excess amount of N2H4 at atmospheric pressure was predicted to be as short as 1.4 × 10−5 s; similarly, a 50–50 mixture of N2O4 and N2H4 at atmospheric pressure decays by half within 4.1 × 10−5 s upon mixing at 300 K, both reflecting the very effective hypergolic initiation of these propellant systems.

Revisiting the tellurium clusters (Ten;n= 2–8) using ab initio methods

The optimized geometries and vibrational frequencies of Te clusters n = 2–8 are calculated using ab initio molecular orbital theory at B3LYP, MP2, BLYP, and BH–HLYP levels of approximation. We found that Te8(D4d) cluster has the highest stability followed by Te7and Te6(D3d). The computed vibrational frequencies have small systematic deviations with IR spectra for crystalline Te5, Te6(C2v). The stability of positively and negatively charged Te clusters is determined by the B3LYP method. This is because the B3LYP method demonstrated the best stability in every cluster geometry. In general, the results showed that the negatively charged clusters have the highest stability, followed by neutral clusters, and finally positively charged clusters. However, the predicted bond angle and bond distance for every cluster geometry displayed very close values with different levels of calculations. These calculations will provide predictions for future experimental studies.

Quantum dynamics calculation of the annihilation spectrum for positron–proline scattering

The annihilation spectrum for positron scattering by the amino acid proline was calculated using local complex potential theory combined with the time-dependent quantum wave packet method. Two nuclear degrees of freedom associated with the motion of the carboxyl group proton were considered in the dynamics. The positronic potential energy surface and positron–electron contact densities were calculated using ab initio multi-component molecular orbital theory. The calculated annihilation spectrum contained several vibrational resonance peaks, which allowed the positron binding energies to be estimated. We also observed a resonance with a very small contribution of zwitterionic proline via proton transfer.

Theoretical Study of the Formation Methane in the Reaction of Methyl Radical with Propanol-2

Theoretical Study of the Formation Methane in the Reaction of Methyl Radical with Propanol-2