Ab initio potential energy surfaces and the corresponding analytical energy functions of the ground 1A' and excited 2A' states for the Li(2(2)P) plus H(2) reaction are constructed. Quasiclassical trajectory calculations on the fitted energy functions are performed to characterize the reactions of Li(2(2)P) with H(2)(v = 0, j = 1) and H(2)(v = 1, j = 1) as well as the reaction when the vibrational energy is replaced by collision energy. For simplicity, the transition probability is assumed to be unity when the trajectories go through the crossing seam region and change to the lower surface. The calculated rotational distributions of LiH(v = 0) for both H(2)(v = 0, j = 1) and H(2)(v = 1, j = 1) reactions are single-peaked with the maximum population at j' = 7, consistent with the previous observation. The vibrational excitation of H(2)(v = 1) may enhance the reaction cross section of LiH(v' = 0) by about 200 times, as compared to a result of 93-107 reported in the experimental measurements. In contrast, the enhancement is 3.1, if the same amount of energy is deposited in the translational states. This endothermic reaction can be considered as an analog of late barrier. According to the trajectory analysis, the vibrational excitation enlarges the H-H distance in the entrance channel to facilitate the reaction, but the excess energy may not open up additional reaction configuration.

The adsorption and dehydrogenation of water on Fe(111), W@Fe(111), and W2@Fe­(111) surfaces have been studied via employing the first-principles calculations method based on the density functional theory. The three adsorption sites of the aforesaid surfaces, such as top (T), 3-fold-shallow (S), and 3-fold-deep (D), were considered. The most favorable structure of all OH x (x = 0–2) species on the surfaces of Fe(111), W@Fe(111), and W2@Fe­(111) have been thoroughly predicted and discussed. Our calculated results revealed that the adsorbed configurations of FeH2O­(T-η1-O)-b, W@FeH2O­(T-η1-O)-a, and W2@FeH2O­(T-η1-O)-a possess energetically the most stable structure with their corresponding adsorption energies of −8.08, −13.37, and −18.61 kcal/mol, respectively. In addition, the calculated activation energies for the first dehydrogenation processes (HO-H bond scission) of H2O on Fe(111), W@Fe(111), and W2@Fe­(111) surfaces are 24.40, 12.62, and 9.97 kcal/mol, respectively. For second dehydrogenation processes (O–H bond scission), the corresponding activation energies of OH on Fe(111), W@Fe(111), and W2@Fe­(111) surfaces are 39.35, 22.69, and 26.24 kcal/mol, respectively. Finally, the entire dehydrogenation courses on the varied Fe(111), W@Fe(111), and W2@Fe­(111) surfaces are exothermic by 20.08, 41.35, and 59.30 kcal/mol, respectively. To comprehend the electronic properties of its nature of interaction between the adsorbate and substrate, we calculated the electron localization functions, local density of states, and Bader charges; the results were consistent and explicable.

The adsorption and dehydrogenation behaviors of ammonia on W(111) surface have been studied by employing spin-polarized density function theory calculations. In this work, three adsorption sites of the W(111) surface were considered, such as top (T), 3-fold-shallow (S), and 3-fold-deep (D) sites. The most stable structures of each NH x (x = 0−3) species on the W(111) surface have been predicted, and the corresponding dehydrogenation processes were found to be via two specific paths (A and B). In PATH A, the calculated activation energies for NH x (x = 1−3) dehydrogenations are 27.66 kcal/mol (for H 2 N−H bond activation), 32.66 kcal/mol (for HN−H bond activation) and 27.84 kcal/mol (for N−H bond activation), respectively, and the entire process is exothermic by 41.63 kcal/mol. On the other hand, in PATH B, the corresponding activation barriers are 35.97, 29.99, and 29.80 kcal/mol, respectively, and the entire process is 42.19 kcal/mol exothermic. To gain more insight into catalytic processes of the aforementioned conducts, the interaction nature between the adsorbate and substrate is analyzed via detailed electronic analysis.

By using a pump-probe technique, the nascent rotational and vibrational state distributions of NaH are obtained in the Na(4 (2)S,3 (2)D, and 6 (2)S) plus H(2) reactions. The rotational distributions for the Na(4 (2)S,3 (2)D) reactions yield a bimodal feature with a major component peaking at J=20-22, similar to that obtained previously in the 4 (2)P reaction, whereas the Na(6 (2)S) reaction gives rise to a distinct distribution with a much lower rotational temperature. The vibrational populations (v=0-4) for these 4 (2)S, 3 (2)D, and 6 (2)S reactions are characterized by corresponding temperatures of 1692+/-120, 819+/-35, and 5329+/-350 K. Due to a significant contribution of configurational mixing between different states with the same symmetry, the collision species initiated from the 4 (2)S and 3 (2)D states are anticipated to track along the entrance surface in a near C(2v) symmetry, then undergo nonadiabatic transition to the inner limb of the reactive 2A(') surface. In contrast, the reaction pathway for the Na(6 (2)S) state with a significantly reduced ionization energy is anticipated to follow a harpoon-type mechanism via a (near) collinear configuration. The increased atomic size of Na may hinder the insertion approach.

The reactions of alkaline earth metal atoms, Mg(3s3p 1P1) and Ca(4s4p 1P1), with H2(v = 1, j) are studied using a pump-probe technique combined with stimulated Raman pumping and coherent anti-Stokes Raman spectroscopy. For the Ca(4 1P1) case, the energy deposited in the v = 1 level enlarges the H2 bond distance to help facilitate the reaction without opening an additional pathway. For the Mg(3 1P1) case, the vibrational excitation of H2 leads to enhancement of the low rotational component of the rotational distribution and the MgH(v = 0)/MgH(v = 1) ratio. These results can be predicted with quasi-classical trajectory calculations and interpreted with a kinematic collision model.

The adsorption and hydrogenation behaviors of hydrogen cyanide to methane and ammonia formation by W(111) catalyst were systematically investigated using the density functional theory method. Based on our calculated consequences, it is found that the WHCN­(T,T-μ2-C,N) is calculated to be the most stable conformer, possessing an adsorption energy of −49.8 kcal/mol, among all calculated structures of HCN/W(111) system. To comprehend the electronic property of its interaction between the adsorbate and substrate, we calculated the electron localization functions, local density of states, and Bader charges; our results were consistent and explicable. Reaction paths in all possible mechanisms were explored in detail, involving the hydrogenation on different orientations of each adsorbate and the scission of the carbon–nitrogen bond. Before forming an imine intermediate (H2CNH(a)), two adsorbed hydrogen atoms will sequentially react with the nitrogen and then carbon atoms in the first and second hydrogenation steps, and the corresponding activation barriers are calculated to be 37.4 and 16.3 kcal/mol, respectively. After yielding an imine intermediate (H2CNH(a)), however, the breaking of carbon–nitrogen bond is likely to proceed at this stage with a pertinent barrier height of 27.5 kcal/mol, forming CH2(a) + NH(a). At elevated temperatures, these resulted adsorbates could be desorbed by further consecutive hydrogenations to generate the final products of methane and ammonia. Our findings provide atomistic-level insight into the novel pathway for surface-assisted synthesis of methane and ammonia via facile hydrogenation reaction of HCN.

In the photodissociation of 1,1-C(2)H(2)Br(2) at 248 nm, the Br(2) elimination channel is probed by using cavity ring-down absorption spectroscopy (CRDS). In terms of spectral simulation, the vibrational population ratio of Br(2)(v = 1)/Br(2)(v = 0) is found to be 0.55+/-0.05, which indicates that the Br(2) fragment is vibrationally hot. The rotational population is thermally equilibrated with a Boltzmann temperature of 349+/-38 K. According to ab initio potential energy calculations, the obtained fragments are anticipated to result primarily from photodissociation of the ground electronic state that undergoes 1) H migration followed by three-center elimination, and 2) isomerization forming either trans- or cis-1,2-C(2)H(2)Br(2) from which Br(2) is eliminated. RRKM calculations predict that the Br(2) dissociation rates through the ground singlet state prevail over those through the triplet state. Measurements of temperature and Ar pressure dependence are examined to support the proposed pathway via internal conversion. The quantum yield for the Br(2) elimination reaction is determined to be 0.07+/-0.04. This result is smaller than that obtained in 1,2-C(2)H(2)Br(2), probably because the dissociation rates are slowed in the isomerization stage.

Hydrogen gas will play an important role in the future since it could be a replacement for gasoline, heating oil, natural gas, and other fuels. In previous reports ammonia (NH3), which has a high hydrogen content, provides a promising mode for the transferring and storing of hydrogen for its on-site generation. Therefore, the dehydrogenation of NH3 on a metal surface has been studied widely in the last few decades. In our study, we employed monolayer tungsten metal to modify the Fe(111) surface, denoted as W@Fe(111), and calculated the adsorption and dehydrogenation behaviors of NH3 on W@Fe(111) surface via first-principles calculations based on density functional theory (DFT). The three adsorption sites of the surface, top (T), 3-fold-shallow (S), and 3-fold-deep (D) were considered. The most stable structure of the NHx (x = 0-3) species on the surface of W@Fe(111) have been predicted. The calculated activation energies for NHx (x = 1-3) dehydrogenations are 19.29 kcal mol(-1) (for H2N-H bond activation), 29.17 kcal mol(-1) (for HN-H bond activation) and 27.94 kcal mol(-1) (for N-H bond activation), and the entire process is exothermic by 33.05 kcal mol(-1). To gain detailed knowledge of the catalytic processes of the NH3 molecule on the W@Fe(111) surface, the physical insights between the adsorbate/substrate interaction and interface morphology were subjected to a detailed electronic analysis.