The low-lying electronic states of Ag3−(1Σg+,3B2), Ag3(2B2,2A1,2B1,4B2,2Σu+,1 2Σg+,2 2Σg+,2Πu,4Σu+), and Ag3+(1A1,1Σg+,3Σu+,3A1) are studied by ab initio calculations with the Stuttgart effective core potentials and corresponding (8s7p6d)/[6s5p3d] and (8s7p5d3f )/[6s5p3d3f] basis sets. The geometries, vibrational frequencies, and energetic splittings are obtained by the coupled-cluster method including singles and doubles (CCSD) and those including up to the noniterative triples [CCSD(T)] correlation methods with additional frozen core molecular orbitals corresponding to 4s and 4p orbitals. The results for well-studied states (Ag3− 1Σg+;Ag3 2B2,2A1,2Σu+;Ag3+ 1A1) are in good agreement with previous experimental results, and therefore our results for other newly studied states are expected to be reliable. The vertical detachment energies of Ag3− are obtained by the electron excitation equation-of-motion coupled-cluster (EE-EOM-CCSD) method and the average deviation from the experimental results is small without any scaling correction of the obtained values. The effect of the f-functions in the basis sets and the noniterative triples in the CCSD(T) method is discussed; the bond lengths are reduced significantly and the vertical detachment energies and ionization potentials are in much better agreement with experiment.

An earlier time-dependent quantum wave packet propagation study of the photochemistry of Ph-OH [J. Chem. Phys. 2005, 122, 224315] is extended to investigate isotope effects (for Ph-OD) and the dynamics initiated by direct (vibronically induced) excitation to the (1)πσ* state. The isotope effect is significant only when the initially excited state is (1)ππ*, that is, there are noticeable changes not only in the time scale but also in the branching ratio (Ã/X̃) for the electronic states of the product Ph-O radical. In contrast, the isotope effect on the dynamics initiated by direct excitation to the (1)πσ* state is very small. Our most important observation for the dynamics initiated by direct excitation to the (1)πσ* state is that the initial excitation of the O-H stretch mode does not result in a noticeable enhancement of the product Ph-O radical in the à state, which corresponds to a dissociating H atom with low kinetic energy. The initial excitation of the CCOH torsion mode is the main reason for the enhancement of the product Ph-O radical in the à state that was observed in a vibrationally mediated two-photon experiment [J. Chem. Phys.2008, 128, 104307].

The photodissociation dynamics of methylamines ͑CH 3 NH 2 and CD 3 ND 2 ͒ on the first electronically excited state has been investigated using the velocity map ion imaging technique probing the H or D fragment. Two distinct velocity components are found in the H͑D͒ translational energy distribution, implying the existence of two different reaction pathways for the bond dissociation. The high H͑D͒ velocity component with the small internal energy of the radical fragment is ascribed to the N-H͑D͒ fragmentation via the coupling of S 1 to the upper-lying S 2 repulsive potential energy surface along the N-H͑D͒ bond elongation axis. Dissociation on the ground S 0 state prepared via the nonadiabatic dynamics at the conical intersection should be responsible for the slow H͑D͒ fragment. Several S 1 vibronic states of methylamines including the zero-point level and n 9 states ͑n =1, 2, or 3͒ are exclusively chosen in order to explore the effect of the initial quantum content on the chemical reaction dynamics. The branching ratio of the fast and slow components is found to be sensitive to the initial vibronic state for the N-H bond dissociation of CH 3 NH 2 , whereas it is little affected in the N-D dissociation event of CD 3 ND 2. The fast component is found to be more dominant in the translational distribution of D from CD 3 ND 2 than it is in that of H from CH 3 NH 2. The experimental result is discussed with a plausible mechanism of the conical intersection dynamics.

Industrially important plasmas offer a variety of complicated molecular processes that benefit from predictive quantum chemical techniques. Ab initio coupled-cluster and MBPT methods are used to characterize structures, vibrational frequencies, ionization potentials, electron affinities, and excited states for the main fragments in the BCl3 plasma, i.e. BCl3, BCl2, BCl, and their anions and cations for which few experimental results exist. The excited, electron attached, and ionized states are calculated by employing the equation-of-motion coupled cluster (EOM-CC) method. Recent results from a photofragmentation study and an electron collision experiment are analysed based on the calculated results. Some features of the potential energy surfaces of excited states of BCl2 are discussed in order to explain the origin of the experimental fluorescence spectrum. We also consider possible microscopic processes with low energy, such as the formation and destruction of neutral and ionic species, decomposition paths, and the role of each fragment. While decomposition through transient states of BCl3− by electron attachment is the most probable path for low-energy electron attachment, decomposition through excited states of BCl3 can play a role only when there is no other way to make the BCl3+ ion.

The low-lying electronic states of Al3 (2A1,2B1,4A2,4B1,2B2,2A1,4B2,6A2) and Al3− (1A1,3B2,3A1,3A2,3B1,5A2) are studied by coupled-cluster methods with a [6s5p2d1f] basis set. The geometries and harmonic frequencies are calculated by the coupled-cluster single double triple (CCSD(T)) correlation method with frozen core and virtual molecular orbitals. The energetic splittings at CCSD(T) geometries are calculated also by the CCSDT method. The calculated vibrational frequencies of the observed states of Al3 (A12, B12, and A24) and Al3− (A11 and B23) are in excellent agreement with experimental results. Other frequencies of this work are expected to be correct within ±20 cm−1. It is shown that A24–B14(E″4) and B22–A12(E′2) of Al3 as well as B23–A13(E′3) and A23–B13(E″3) of Al3− are pairs of minima and transition states on a potential energy surface of a pseudorotation of the corresponding degenerate states. The vertical excitation energies of additional states of Al3(2E′,4E′,2A1′) and Al3−(1E″,1E′) are calculated by the electron-excitation equation-of-motion CC method and the electron-attachment equation-of-motion CC method. The possible processes of ionizations and vibronic transitions are analyzed based on the calculated results. All features of the recent photoelectron spectroscopic study of Al3− are explained consistently. It is also shown that the photoelectron signals of electron binding energies of 2.65 and 4.4 eV in earlier experiments correspond to the ionization of the ground state of Al3− to higher-lying excited states of Al3. The two states of the resonant two-photon ionization experiment are assigned to the lowest quartet state and the third quartet state, E″4→E′4, without ambiguity. The anticipated features of five more electronic excitations with transition energies of 0.22, 0.69, 0.77, 0.98, and 1.06 eV are discussed.

A very simple equation, F=[(∂(V-V)/∂Q)/(V-V)]/2, giving a reliable magnitude of non-adiabatic coupling terms (NACTs, F's) based on adiabatic potential energies only (V and V) was discovered, and its reliability was tested for several prototypes of same-symmetry interstate crossings in LiF, C, NHCl, and CHSH molecules. Our theoretical derivation starts from the analysis of the relationship between the Lorentzian dependence of NACTs along a diabatization coordinate and the well-established linear vibronic coupling scheme. This analysis results in a very simple equation, α=2κ/Δ, enabling the evaluation of the Lorentz function α parameter in terms of the coupling constant κ and the energy gap Δ (Δ=|V-V| ) between adiabatic states at the crossing point Q. Subsequently, it was shown that Q corresponds to the point where F exhibit maximum values if we set the coupling parameter as κ=[(V-V)⋅(∂(V-V)/∂Q)]/2. Finally, we conjectured that this relation could give reasonable values of NACTs not only at the crossing point but also at other geometries near Q. In this final approximation, the pre-defined crossing point Q is not required. The results of our test demonstrate that the approximation works much better than initially expected. The present new method does not depend on the selection of an ab initio method for adiabatic electronic states but is currently limited to local non-adiabatic regions where only two electronic states are dominantly involved within a nuclear degree of freedom.

The photodissociation dynamics of thiophenol (PhSH) excited to the 1(1) ππ* state was investigated by time-dependent quantum wavepacket propagation within two-dimensional (2D) space consisting of the S-H bond and -SH torsion. We systematically studied the dependence of the branching ratio (Ã/X(~)) between the two electronic states of the phenylthiyl radical (PhS(.) ) on several factors of the 2D potential energy surfaces (PESs). The effect of a reduced initial barrier to the first ππ*/πσ* conical intersection (CI) was found to be marginal, whereas the effects of a reduced torsional barrier of -SH on the excited ππ* state and the mitigated slope of the πσ* PES between the first (ππ*/πσ*) and the second (πσ*/S0 ) CIs were noticeable. The effect of the slope on the branching ratio has never been previously noticed. It was shown that the branching ratio can be sufficiently above unity without pre-excitation of the torsion mode of -SH, which has been assumed so far.

The geometries and vibrational properties of the low-lying electronic states of neutral and anionic of M 3 (M ) P, As, Sb, and Bi) are studied using the coupled-cluster singles, doubles, and noniterative triples (CCSD(T)) method as well as the density functional theory (B3LYP-DFT) method. For P 3 -, the 1 Σ g + and X 3 A′ 1 (D 3h ) states are almost degenerate. The X 3 A′ 1 (D 3h ) state, however, turns out to be the lowest state for As 3 -, Sb 3 -, and Bi 3 -, and the adiabatic excitation energies of the 1 Σ g + state are 0.6, 0.9, and 1.0 eV, respectively. In the anionic trimers of all four elements, another singlet state, 1 A 1 (C 2V ), is located about 0.3-0.4 eV above X 3 A′ 1 (D 3h ); the energy gap between these states is compared to the splittings between the first two peaks in the photoelectron spectra of these anions. For all of the neutral trimers, the adiabatic and vertical energetic splittings between the Jahn-Teller components of the X 2 E′′ and 4 E′ states are calculated to be only 0.04-0.08 eV. Another quartet state, 4 A′′ 2 , is 0.4 eV higher, almost equal, 0.2 eV lower, and 0.3 eV lower in energy than the 4 E′ state in P 3 , As 3 , Sb 3 , and Bi 3 , respectively. All of the features of the main peaks in the photoelectron spectra of the anions observed to date are explained by using calculated geometries, vibrational frequencies, and excitation energies. In addition, a number of peaks are predicted that have not yet been observed experimentally.