A theoretical study on the photodissociation of C3O2

The photodecomposition of C₃O₂ into C₂O and CO is studied with the ab initio MO calculation. It is found that, starting from the second excited state of C₃O₂ (_u), the ground-state C₂O (triplet) is yielded through the bent dissociation. The stable structure of the excited triplet state of C₃O₂ as an intermediate is also demonstrated.     

First observation of clusters for solvated tropylium ions

We have first observed clusters for solvated tropylium ions (Tr+(ROH)n) which were isolated from ROH-CH3CN (1:1 by vol.; R = Me, Et, and Prn) solutions by using a specially designed mass spectrometer and found the clear-cut essential features concerning the solvation structure around Tr+.     

A note on the theory of interatomic long-range forces

A comment is made on the multipolar expansion formula of the long-range force between hydrogen atoms previously obtained. The second-order perturbation energy neglecting exchange in the framework of the Unsöld approximation is evaluated exactly. An extension is made to helium atoms, and to other s-electron interactions. An approximate method is suggested to estimate the interatomic force between two atoms in general.     

A computational study on addition of Grignard reagents to carbonyl compounds

The mechanism of stereoselective addition of Grignard reagents to carbonyl compounds has been investigated using B3LYP density functional theory calculations. The study of the reaction of methylmagnesium chloride and formaldehyde in dimethyl ether revealed a new reaction path involving carbonyl compound coordination to magnesium atoms in a dimeric Grignard reagent. The structure of the transition state for the addition step shows that an interaction between a vicinal-magnesium bonding alkyl group and C=O causes the C-C bond formation. The simplified mechanism shown by this model is in accord with the aggregation nature of Grignard reagents and their high reactivities toward carbonyl compounds. Concerted and four-centered formation of strong O-Mg and C-C bonds was suggested as a polar mechanism. When the alkyl group is bulky, C-C bond formation is blocked and the Mg-O bond formation takes precedence. A diradical is formed with the odd spins localized on the alkyl group and carbonyl moiety. Diradical formation and its recombination were suggested to be a single electron transfer (SET) process. The criteria for the concerted polar and stepwise SET processes were discussed in terms of precursor geometries and relative energies.     

Gas-phase ion/molecule reactions in C5F8

Gas-phase ion-molecule reactions in octafluorocyclopentene (C5F8) were studied with a pulsed electron beam mass spectrometer. When a few Torr of major gas, CH4, Ar, or N2, containing approximately 10 mTorr C5F8 was ionized by 2 keV electrons, C5F8+, C5F7+, C4F6+, C4F5+, and C3F3+ were formed as major fragment ions. The interaction between those ions and C5F8 is found to be a weak electrostatic interaction. The cation...C5F8 bonding energies are around 10 kcal/mol, which were reproduced well by (U)B3LYP/6-311+G(d) calculations. The proton affinity of C5F8 (=148.6 kcal/mol by B3LYP/6-311+G(d)) was found to be smaller than that of C2H4 (=162.8 kcal/mol). In the negative mode of operation, the intense signal of C5F8- was observed during the electron pulse. This indicates that C5F8 has a positive electron affinity (1.27 eV by (U)B3LYP/6-311+G(d)). The C5F8- ion was quickly converted to a complex C10F16-. This complex did not react further with C5F8 down to 170 K. The theoretical calculation revealed that a C5F7-F-...C5F8 interaction mode in (C5F8)2- was converted to a C5F7*...C5F9- one via fluoride-ion transfer. The F- ion was found to form a strong covalent bond with C5F8, but the interaction in F-(C5F8)- - -C5F8 is a weak electrostatic interaction due to the charge dispersal in F-(C5F8). The halide ions except F- interact with C5F8 only weakly. Thermochemical stabilities for the cluster ions I-(CH3I)n (n = 1, 2) were also determined.     

Atmospheric pressure chemical ionization of explosives using alternating current corona discharge ion source

The high‐sensitive detection of explosives is of great importance for social security and safety. In this work, the ion source for atmospheric pressure chemical ionization/mass spectrometry using alternating current corona discharge was newly designed for the analysis of explosives. An electromolded fine capillary with 115 µm inner diameter and 12 mm long was used for the inlet of the mass spectrometer. The flow rate of air through this capillary was 41 ml/min. Stable corona discharge could be maintained with the position of the discharge needle tip as close as 1 mm to the inlet capillary without causing the arc discharge. Explosives dissolved in 0.5 µl methanol were injected to the ion source. The limits of detection for five explosives with 50 pg or lower were achieved. In the ion/molecule reactions of trinitrotoluene (TNT), the discharge products of NO_x^? (x = 2,3), O₃ and HNO₃ originating from plasma‐excited air were suggested to contribute to the formation of [TNT ? H]^? (m/z 226), [TNT ? NO]^? (m/z 197) and [TNT ? NO + HNO₃]^? (m/z 260), respectively. Formation processes of these ions were traced by density functional theory calculations. Copyright © 2015 John Wiley & Sons, Ltd.     

Electronic-phase transition associated with instability of the Hartree–Fock solution of infinite one-dimensional system

Electronic-phase transition associated with the singlet instability problem of the Hartree-Fock solution of the extended system is studied employing the metallic trans-polyacetylene. Concerning the eigenstates of the stability matrix set up for the crystal orbitals at the Fermi level, classification of the electronic phases is attempted and the origin of their emergence in relation to the interelectronic interaction is discussed.     

Hydrogen bonds in gas-phase clusters between halide ions and olefins

Gas-phase clustering reactions of halide ions (X- = F-, Cl-, Br-, and I-) with ethylene (C2H4) and propylene (C3H6) were studied with a pulsed electron beam mass spectrometer. Bonding energies of all cluster ions were found to be less than 10 kcal/mol, i.e., no anion-initiated polymerization of C2H4 and C3H6 took place. For the cluster F-(C2H4)n, a small gap in the binding energy is observed between n = 4 and 5 suggesting that the first shell is completed with n = 4. For larger halide ions, the bond energies for the clusters X-(C2H4)n were found to be nearly n independent. For Cl-(C3H6)n a steep decrease in binding energies was observed between n = 2 and 3 and n = 3 and 4. The structure of the cluster ions was investigated by ab initio calculations. X-(C2H4)n complexes were calculated to have hydrogen-bond geometries regardless of the identity of the halide ions, and bidentate (chelate) type geometries of X-(C3H6)1 were found.     

The key Cl− ligand for metal‐to‐ligand charge transfer in mononuclear terpyridine ruthenium(II) and binuclear ruthenium(II) tetrapyridylpyrazine complexes

Electronic structures of binuclear ruthenium complexes [Ru₂(terpy)₂(tppz)]⁴⁺ ( 1A ) and [Ru₂Cl₂(L)₂(tppz)]²⁺ {L = bpy ( 2A ), phen ( 3A ), and dpphen ( 4A )} were studied by density functional theory calculations. Abbreviations of the ligands (Ls) are bpy = 2,2′‐bipyridine, phen = 1,10‐phenanthroline, dpphen = 4,7‐diphenyl‐1,10‐phenanthroline, terpy = 2,2′:6′,2″‐terpyridine, and tppz = tetrakis(2‐pyridyl)pyrazine. Their mononuclear reference complexes [Ru(terpy)₂]²⁺ ( 1B ) and [RuClL(terpy)]⁺ {L = bpy ( 2B ), phen ( 3B ), and dpphen ( 4B )} were also examined. Geometries of these mononuclear and binuclear Ru(II) complexes were fully optimized. Their geometric parameters are in good agreement with the experimental data. The binuclear complexes were characterized by electrospray ionization mass spectrometry, UV–Vis spectroscopy, and cyclic voltammograms. Hexafluorophosphate salts of binuclear ruthenium complexes of 3A and 4A were newly prepared. The crystal structure of binuclear complex 1A (PF₆)₄ was also determined. Orbital interactions were analyzed to characterize the metal‐to‐ligand charge‐transfer (MLCT) states in these complexes. The Cl^? ligand works to raise the orbital energy of the metal lone pair, which leads to the low MLCT state. Copyright © 2011 John Wiley & Sons, Ltd.