Intrinsic Reaction Coordinate Analysis of the Activation of CH4 by Molybdenum Atoms: A Density Functional Theory Study of the Crossing Seams of the Potential Energy Surfaces

Investigation on spin-flip reaction of Re + CH3CN by relativistic density functional theory

To explore the integrated reaction mechanisms for Re atom with acetonitrile theoretically, density functional theory with zero-order regular approximation (ZORA) relativistic corrections has been employed at the BP86/TZ2P level. There have been three adiabatic potential energy surfaces in the study along sextet, quartet and doublet spin states. However, the detailed minimum energy reaction pathway altogether contains six stationary states () to (), five transition states (), and two intersystem crossings with spin inversion (marked by ⇒): (6)Re + CH3CN → η(1)-ReNCCH3 () → ⇒ η(2)-Re(NC)CH3 () → → η(3)-HRe(NCCH2) () → → CH3-ReNC () → → CH2[double bond, length as m-dash]Re(H)NC () ⇒ → CH[triple bond, length as m-dash]Re(H)2NC (). Thereinto, the lowest energy crossing points (LECP) have been determined by the DFT fractional-occupation-number (FON) approach. The first spin inversion has transferred the potential energy surfaces from high-spin sextet to the quartet intermediate () with the subsequent C-C bond breakage. The second one from the quartet to the low-spin doublet state accompanies the C-H activation, decreasing the transition barrier by 157 kJ mol(-1). The overall reaction could be exothermic by about 210 kJ mol(-1). Harmonic vibration frequencies and NBO, WBO analysis are also applied to verified the experimental observed information.

Theoretical investigation of atomic oxygen erosion mechanisms of 1,3-didecyl cyclopentane, 1,3-dioctyldodecyl cyclopentane and alkylated cyclopentane

Atomic oxygen erosion mechanisms of 1,3-didecyl cyclopentane, 1,3-dioctyldodecyl cyclopentane and alkylated cyclopentane.

Spin-flip reactions of Zr + C2H6 researched by relativistic density functional theory

Density functional theory (DFT) with relativistic corrections of zero-order regular approximation (ZORA) has been applied to explore the reaction mechanisms of ethane dehydrogenation by Zr atom with triplet and singlet spin-states. Among the complicated minimum energy reaction path, the available states involves three transition states (TS), and four stationary states (1) to (4) and one intersystem crossing with spin-flip (marked by -->): (3) Zr + C 2 H 6 → (3) Zr-CH 3 -CH 3 ((3)1) → (3)TS 1/2 → (3) ZrH-CH 2 -CH 3 ((3)2) → (3) TS 2/3 --> (1) ZrH2-CH2 = CH2 ((1) 3) → (1) TS 3/4 → (1) ZrH 3 -CH = CH 2 ((1)4). The minimum energy crossing point is determined with the help of the DFT fractional-occupation-number (FON) approach. The spin inversion leads the reaction pathway transferring from the triplet potential energy surface (PES) to the singlet's accompanying with the activation of the second C-H bond. The overall reaction is calculated to be exothermic by about 231 kJ mol(-1). Frequency and NBO analysis are also applied to confirm with the experimental observed data.

Ab initio molecular dynamics study of the reaction of U+ and U2+ with H2O in the gas phase: direct classical trajectory calculations

The gas phase reactions of U(+) and U(2+) with H2O were investigated using an ab initio molecular dynamics method. All of the information along the minimum energy path were calculated with density functional theory (DFT) and coupled cluster methods. For U(+) with H2O, the molecular dynamics simulations yield a branching ratio of 86% for the H2 elimination channel to 14% for the H atomic elimination channel in agreement with the quadruple ion trap mass spectrometry (QIT/MS) experimental ratio of 91% to 9%. In the case of U(2+) + H2O, there is a crossing of the potential energy surfaces (PES) after the first transition state. Crossing seams between the PES and possible spin inversion processes were studied by means of the intrinsic reaction coordinate (IRC) approach. For U(2+) with H2O, all trajectories are corresponds to H atom elimination channel, this is consistent with the Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) experimental results. The chemical bonding evolution along the reaction pathways was discussed by using topological methodologies of the electron localization function (ELF).

Investigation of spin-flip reactions of Zr + CH3CN by relativistic density functional theory

To explore the details of the reaction mechanisms of Zr atoms with acetonitrile molecules, the triplet and singlet spin-state potential energy surfaces have been investigated. Density functional theory (DFT) with the relativistic zero-order regular approximation at the PW91/TZ2P level has been applied. The complicated minimum energy reaction path involves four transition states (TS), stationary states 1-5 and one spin inversion (indicated by ⇒): (3)Zr + NCCH(3) → (3)Zr-η(1)-NCCH(3) ((3)1) → (3)TS(1/2) → (3)Zr-η(2)-(NC)CH(3) ((3)2) → (3)TS(2/3) → (3)ZrH-η(3)-(NCCH(2)) ((3)3) → (3)TS(3/4) → CNZrCH(3) ((3)4) ⇒ (1)TS(4/5) → CN(ZrH)CH(2) ((1)5). The minimum energy crossing point was determined with the help of the DFT fractional-occupation-number approach. The spin inversion leading from the triplet to the singlet state facilitates the activation of a C-H bond, lowering the rearrangement-barrier by 78 kJ/mol. The overall reaction is calculated to be exothermic by about 296 kJ/mol. All intermediate and product species were frequency and NBO analyzed. The species can be rationalized with the help of Lewis type formulas.

Investigation of spin-flip reactions of Nb + CH3CN by relativistic density functional theory

In order to explore the details of the reaction mechanisms of Nb atoms with acetonitrile molecules, the sextet, quartet, and doublet spin state potential energy surfaces have been investigated. Density functional theory (DFT) with the relativistic zero-order regular approximation at the PW91/TZ2P level has been applied. The complicated minimum energy reaction path involves four transition states (TS), stationary states (1) to (5) and two intersystem crossings from spin sextets to quartets to doublets (indicated by ⇒): (6)Nb + NCCH3→(6)Nb η(1)-NCCH3 ((6)1) →(6)TS1/2⇒(4)Nb η(2)-(NC)CH3 ((4)2) →(4)TS2/3→(4)NbH η(3)-(NCCH2) ((4)3) →(4)TS3/4→ CNNbCH3 ((4)4) ⇒(2)TS4/5→ CN(NbH)CH2 ((2)5). The minimum energy crossing points were determined with the help of the DFT fractional-occupation-number approach. The first spin inversion leads from the sextet to an energetically low intermediate quartet ((4)2) with final insertion of Nb into the C-C bond. The second one from the quartet to the doublet state facilitates the activation of a C-H bond, lowering the rearrangement-barrier by 44 kJ mol(-1). The overall reaction is calculated to be exothermic by about 170-180 kJ mol(-1). All intermediate and product species were frequency and NBO analyzed. The species can be rationalized with the help of Lewis type formulas.

Metal-organic charge transfer can produce biradical states and is mediated by conical intersections

The present paper illustrates key features of charge transfer between calcium atoms and prototype conjugated hydrocarbons (ethylene, benzene, and coronene) as elucidated by electronic structure calculations. One- and two-electron charge transfer is controlled by two sequential conical intersections. The two lowest electronic states that undergo a conical intersection have closed-shell and open-shell dominant configurations correlating with the 4s(2) and 4s(1)3d(1) states of Ca, respectively. Unlike the neutral-ionic state crossing in, for example, hydrogen halides or alkali halides, the path from separated reactants to the conical intersection region is uphill and the charge-transferred state is a biradical. The lowest-energy adiabatic singlet state shows at least two minima along a single approach path of Ca to the π system: (i) a van der Waals complex with a doubly occupied highest molecular orbital, denoted Φ(2)(1), and a small negative charge on Ca and (ii) an open-shell singlet (biradical) at intermediate approach (Ca...C ≈2.5-2.7 Å) with molecular orbital structure (1)(2), where (2) is an orbital showing significant charge transfer form Ca to the π-system, leading to a one-electron multicentered bond. A third minimum (iii) at shorter distances along the same path corresponding to a closed-shell state with molecular orbital structure has also been found; however, it does not necessarily represent the ground state at a given CaC distance in all three systems. The topography of the lowest adiabatic singlet potential energy surface is due to the one- and two-electron bonding patterns in Ca-π complexes.