Daiwei Liao

Ab initio study of the n-pi(*) electronic transition in acetone: Symmetry-forbidden vibronic spectra

Ab initio calculations of geometry and vibrational frequencies of the first singlet excited 1A2(1A″) state of acetone corresponding to the n-π* electronic transition have been carried out at the CASSCF/6-311G** level. The major geometry changes in this state as compared to the ground state involve CO out-of-plane wagging, CO stretch and torsion of the methyl groups, and the molecular symmetry changes from C2v to Cs. The most pronounced frequency changes in the 1A″ state are the decrease of the CO stretch frequency v3 by almost 500 cm−1 and the increase of the CH3 torsion frequency v12 from 22 to 170 cm−1. The optimized geometries and normal modes are used to compute the normal mode displacements which are applied for calculations of Franck–Condon factors. Transition matrix elements over the one-electron electric field operator at various atomic centers calculated at the state-average CASSCF/6-311+G** level are used to compute vibronic couplings between the ground 1A1, 1A2, and Rydberg 1B2(n-3s), 2 1A1(n-3...

Deuterium Inverse Isotopic Effect in Ammonia Synthesis over Ru-Based and Fe-Based Catalysts

Abstract The deuterium inverse isotopic effect (DIIE) is important for the clarification of the ammonia synthesis mechanism over transition metal catalysts. We investigated the DIIE over Ru-based and Fe-based catalysts including pure Fe, multi-promoted fused Fe, pure Ru, Ru/γ-Al 2 O 3 , K-Ru/γ-Al 2 O 3 , Ru/MgO, K-Ru/MgO, and Ba-Ru/MgO under the reaction conditions of N 2 /H 2 (or D 2 ) volume ratio = 1/3, 0.2 MPa, 633–733 K, and GHSV = 24 000 and 12 000 h −1 . A strong DIIE ( r D / r H of about 2) was observed over the above catalysts. The trend of the DIIE with catalysts and temperature indicated a strong competition between the dynamic and thermodynamic factors.

Supported Catalysts with Ru-M (M=Fe,Co,Ni,Mo) Bimetallic Active Centers for Ammonia Synthesis

Abstract Supported Ru-M (M = Fe, Co, Ni, Mo) bimetallic active center catalysts with a potassium promoter for the ammonia synthesis were studied. The activity of the Ru-Co catalyst is the highest, and the activity of the Ru-Mo catalyst is the lowest. When the Ru loading decreases by half (from 4% to 2%), the Ru-Co catalyst with a Co loading of 2% is the most valuable and exhibits an activity almost the same as the catalyst with 4% Ru and 4% Co. The Ru-Co catalysts with Ru and Co loadings of 2% each supported on Mg-Al complex oxide, MgAl 2 O 4 spinel, and MgO were also studied. The catalyst supported on MgO calcined at 600°C has the highest activity.

Computer-aided molecular design of catalysts based on mechanism and structure

A bridge theory including a mathematical expression for the process of catalysis is proposed. A catalytic reaction can be expressed as ||reactant matrix|| × ||bridge matrix|| = ||product matrix||. The physicochemical bases of computer-aided molecular design of catalysts are discussed. Five variations on both structure and mechanism are identified as important in the process of catalyst design. An expert system of molecular design of catalysts (ESMDC) including a knowledge base and a reasoning scheme has been developed and is described.

Two-photon vibronic spectroscopy of allene at 7.0–10.5 eV: experiment and theory

2 + 1 resonance-enhanced multiphoton ionization (REMPI) spectra of allene at 7.0–10.5 eV have been observed. The excited vibronic symmetry has been determined from polarization-ratio measurements. Based on the vibronic energies and peak intensities calculated using ab initio MO and time-dependent density functional theory, the very congested REMPI spectra have been assigned as due to π* ← π, 3p ← π, 4s ← π, 4p ← π, and 4d ← π transitions. Vibrational progressions related to the CH2 twisting (ν4 ∼770 cm−1) have been observed for several excited electronic states. Calculated Franck–Condon factors also confirm that CH2 twisting is the most active mode in the vibronic spectra of allene. In this study, theoretical calculations of two-photon intensities and polarization ratios have been made through the ab initio computed one-photon transition dipole moments to various electronic states as intermediates. As a starting point to interpret the complicated vibronic spectrum of allene, the theoretical approach, without vibronic couplings, has been applied to predict the peak positions, spectral intensities, and polarization ratios of Rydberg states, and qualitatively shows a considerable agreement with experimental observations.