Time-Dependent Density Functional Theory (TD-DFT) has become the most widely-used theoretical approach to simulate the optical properties of both organic and inorganic molecules. In this contribution, we review TD-DFT benchmarks that have been performed during the last decade. The aim is often to pinpoint the most accurate or adequate exchangecorrelation functional(s). We present both the different strategies used to assess the functionals and the main results obtained in terms of accuracy. In particular, we discuss both vertical and adiabatic benchmarks and comparisons with both experimental and theoretical reference transition energies. More specific benchmarks (oscillator strengths, excited-state geometries, dipole moments, vibronic shapes, etc.) are summarized as well. V C 2013 Wiley Periodicals, Inc.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/qua.24438

TD-DFT benchmarks: A review

1. Understanding chemical reactions at the molecular level 2. Molecular collisions 3. Introduction to reactive molecular collisions 4. Scattering as a probe of collision dynamics 5. Introduction to polyatomic dynamics 6. Structural considerations in the calculation of reaction rates 7. Photoselective chemistry: access to the transition state region 8. Chemistry in real time 9. State-changing collisions: molecular energy transfer 10. Stereodynamics 11. Dynamics in the condensed phase 12. Dynamics of gas-surface interactions and reactions.

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Molecular reaction dynamics

Molecular Reaction Dynamics: Frontmatter

The C2H5• + O2 reaction, central to ethane oxidation and thus of fundamental importance to hydrocarbon combustion chemistry, has been examined in detail via highly sophisticated electronic structure methods. The geometries, energies, and harmonic vibrational frequencies of the reactants, transition states, intermediates, and products for the reaction of the ethyl radical (X 2A‘) with O2 (X 3 , a 1Δg) have been investigated using the CCSD and CCSD(T) ab initio methods with basis sets ranging in quality from double-zeta plus polarization (DZP) to triple-zeta plus double polarization with f functions (TZ2Pf). Five mechanisms (M1−M5) involving the ground-state reactants are introduced within the context of previous experimental and theoretical studies. In this work, each mechanism is systematically explored, giving the following overall 0 K activation energies with respect to ground-state reactants, Ea(0 K), at our best level of theory:  (M1) direct hydrogen abstraction from the ethyl radical by O2 to give e...

The C2H5 + O2 Reaction Mechanism: High-Level ab Initio Characterizations

Methanotrophs are bacteria that live on methane as their only source of carbon.1 The first step in their utilization of this simplest of all hydrocarbons is its selective conversion to methanol. Subsequent biochemical pathways transform methanol to formaldehyde, which in turn is processed into biomass. Further oxidation of formaldehyde to carbon dioxide provides energy that is stored for later use as NADH.2 The conversion of methane to methanol is catalyzed at the active site of a metalloenzyme known as methane monooxygenase, or MMO.3-9

Mechanistic studies on the hydroxylation of methane by methane monooxygenase.

Multiphoton ionization (MPI) spectroscopy is rapidly evolving into a valuable adjunct to VUV spectroscopy for the study of the highly excited states of molecules. The technique is described, and several examples are given of its applications. Studies of the 3pz Rydberg states of the methylbenzenes and of the 1B2u state of benzene show that state assignments can be made and new multiphoton structure seen that is not available in one-photon spectra. MPI of benzene in a supersonic jet demonstrates dramatic resolution improvement and shows that natural linewidth information can be gained for large molecules. Collisional effects in MPI spectra are briefly discussed with reference to Xe and to laser enhanced collisional broadening of nitric oxide in the supersonic beam.

Molecular multiphoton ionization spectroscopy

A resonance seen in the multiphoton ionization spectrum of benzene at 391.4 nm is identified as a two‐photon resonance with a bound state at 51 085 cm−1. This state has probable symmetry 1E1g or 1E2g as indicated by an active e2g vibration. No other allowed two‐photon transitions are seen below this energy. Three‐photon resonances with the Rydberg states of benzene are seen and compared to the one‐photon absorption spectrum. The great similarity indicates a strong 1A1g component in the two‐photon virtual state. Two‐photon resonances with the 1B2u state agree with two‐photon fluorescence excitation spectra but show no diminution above the energy where fluorescence is quenched.

The multiphoton ionization spectrum of benzene

Rate equation modelling of molecular multiphoton ionization dynamics

A new method for the high‐resolution electronic spectroscopy of cations with mass resolution. Optical transitions from Rydberg states converging on the ground state of the cation to states with electronically excited cores are detected by their rapid autoionization. The spectrum of these transitions provide ionic information because the photoabsorption cross‐section of a molecule in a high‐n Rydberg state closely mirrors the spectrum of the ion core. The technique presented here, called photoinduced Rydberg ionization (PIRI) spectroscopy, is applied in this case to record the B 2E2g→X 2E1g transition of the benzene cation via the vibrational origin of the X 2E1g ionic state.

Philip M. Johnson

Papers

Molecular multiphoton ionization spectroscopy

The multiphoton ionization spectrum of benzene

Rate equation modelling of molecular multiphoton ionization dynamics

Photoinduced Rydberg ionization spectroscopy

The discovery of a 3p rydberg state in benzene by three-photon resonant multiphoton ionization spectroscopy