Ko Saito

Thermal unimolecular decomposition of formic acid

The initial steps involved in the thermal decomposition of formic acid in the temperature range of 1370–2000 K have been investigated by monitoring the IR emission intensities at 3.4 and 4.6 μm, corresponding to the reactant and carbon monoxide, respectively, behind reflected shock waves in mixtures diluted in Ar (0.1–1.5 mol%, total densities 5.3×10−6–3.2×10−5 mol cm−3). It was found that the decomposition proceeded via channel (1) HCOOH+Ar→CO+H2O+Ar dominantly and the contribution of channel (2) HCOOH+Ar→CO2+H2+Ar was very small. An Arrhenius expression of the second order rate constant was obtained as k1,0 =1014.32  exp(−40.4 kcal mol−1/RT) cm3 mol−1 s−1. Ab initio calculations were performed for probable transition states (TS) of channels (1) and (2). The results showed that the potential energy for a TS of channel (1) was lower than that of channel (2) by 20–30 kcal mol−1. On the basis of a RRKM weak collision, k2,0 values were estimated which was smaller than k1,0 by about two orders, being consiste...

Molecular orbital calculations of the substituent effect on intermolecular CH/π interaction in C2H3X-C6H6 complexes (X=H, F, Cl, Br, and OH)

Abstract The effect of a substituent group in dimeric complexes of benzene with ethylene and its four derivatives on the intermolecular CH/π interaction was studied theoretically. The hydrogen-bonding nature of the CH/π interaction is confirmed by the bond critical point analysis within the atoms-in-molecules (AIM) theory. It has been found that the CH⋯π access angle depends on the exchange repulsion and the induction effect from the substituent group. The effect of the charge transfer interaction by the substituent group is energetically insignificant. However, the charge density can be varied by substitution, and this contribution cannot be ignored.

Basis set superposition error free self-consistent field method for molecular interaction in multi-component systems : Projection operator formalism

The self-consistent field method for molecular interaction (SCF MI) by Gianinetti, Raimondi, and Tornaghi is extended to multi-component systems. A set of equations are written with projection operators, and the accurate approximate equations are derived. The method is applied to water clusters and to a fluoride anion complex with a water dimer. The calculated interaction energies are compared with those estimated with the counterpoise method, and they converge to smaller values for extensive basis sets. The underestimation of the binding energy results from the omission of the most part of charge transfer contribution in the wave function.

Reactions of N(4S) atoms with NO and H2

Reactions of N(4S) atoms with NO and H2 have been investigated using direct detection of N atoms by the atomic resonance absorption technique in a shock tube apparatus, where N(4S) is generated by photodecomposition of NO by 193 nm laser radiation behind reflected shock waves. The rate constant of the reaction, N+NO→N2+O (1) has been determined using pseudo first‐order kinetic analysis to be k1=(1.3±0.3)×1013 (cm3 mol−1 s−1) over 1600–2300 K temperature range, which agrees very well with the estimation by Baulch et al. [Evaluated Kinetic Data for High Temperature Reactions (Butterworths, London, 1973), Vol. 2]. No (or very small) activation energy of this process was confirmed. Also, the rate constant of the reaction, N+H2→NH+H (2) has been decided by adding H2 to NO–Ar mixtures; it is k2=(2.8±0.2)×1014 exp(−Ea/RT) (cm3 mol−1 s−1), where Ea =33±7 kcal/mol. A quantum mechanical calculation performed in order to determine the mechanism of this reaction suggests that the reaction N(4S)+H2→NH+H proceeds via a...

Theoretical molecular Auger spectra with electron population analysis

Abstract An approximation method is proposed to simulate the molecular Auger spectra. Auger transition rates are estimated with atomic populations of valence orbitals on an excited atom by Mulliken and Lowdin population analyses. Normal Auger energies and relative rates for H 2 O and NH 3 molecules are evaluated using a full CI wave functions among the valence orbitals constructed from SCF orbitals for the neutral ground state and for the core-hole excited state. Theoretical spectra show fairly good correspondence with the experimental spectra. It is demonstrated that the present approach is applicable for qualitative assignment and analysis of Auger spectra for larger molecules.

Photodissociation of ICl at 235–248 nm

Photodissociation of iodine monochloride has been investigated at 235–248 nm by studying Doppler profiles of (2+1) resonance enhanced multiphoton ionization spectra of fragment chlorine atoms and two‐photon laser induced fluorescence spectra of iodine atoms. At 235.3–237.8 nm, a measured branching ratio of [Cl*(2P1/2)]/[Cl(2P3/2)] is 0.68±0.10. At 248 nm, the [I*(2P1/2)]/[I(2P3/2)] ratio is 0.71±0.27. From the measured Doppler profiles and the ab initio calculation, the photoprepared states leading to Cl and Cl* production are assigned to the 3Π0+ (and possibly 3∑−0+) and the 1Π1 states, respectively. Nonadiabatic couplings between the potential curves have been discussed.

Mechanism of ion desorption reaction of PMMA thin film induced by core excitation

Abstract Auger electron spectra of PMMA (poly-methylmethacrylate) which show remarkable site-specific ion desorption are calculated using ab initio molecular orbital (MO) calculation and compared with the results of Auger electron-photoion coincidence experiments. Methyl isobutyrate and its trimer are used as model molecules of PMMA. The calculation is based on the single configuration state function and limited configuration interaction methods, and Auger transition probabilities are estimated by overlap between core and valence MOs. The calculated normal Auger spectra obtained on specific atoms reproduce well the experimental resonant Auger spectra for both the carbon and oxygen sites. The careful analysis of the calculated Auger spectra indicates that the desorption of CHn+ ions is strongly concerned with the Auger final states which have holes in the O–CH3 bonding orbitals.

The molecular structure of acyclic aralkyl compounds studied by a crystallographic database survey. Relevance of the intramolecular CH/π hydrogen bond to conformation

A database study was carried out, by the use of the Cambridge Structural Database, to investigate the conformation of aralkyl compounds ArCH2XCH2Y 1 and ArCHCH3XCH 2 in crystals. The structure bearing R (R: any group) and Ar in the syn relationship has often been found in these compounds. The proportion of crystal structures bearing R and Ar in the syn relationship relative to the anti conformation (rsyn/anti) varied from 0.55 for 1 to 3.68 for 2. The logarithm of rsyn/anti was plotted against the difference in Gibbs energy ΔGsyn − anti obtained by MO calculations of model compounds at the MP2/6-311G(d,p)//MP2/6-31G(d) level: C6H5CH2XCH3 and C6H5CHCH3XCH3. A linear correlation has been shown between lnrsyn/anti and ΔGsyn − anti. The CH/π interaction is suggested to operate in controlling the R/Ar-folded crystal structure of these aralkyl compounds.

Thermal unimolecular decomposition of formyl fluoride in Ar

Abstract The thermal decomposition of formyl fluoride in Ar has been studied behind shock waves over the temperature range 1160–1480 K and the total density range (7.18–18.6) × 10 −6 mol cm −3 . The decomposition was monitored by means of IR emission from the CH stretching of the reactant and the fundamental band of the CO produced. The decomposition was found to be molecular elimination producing HF and CO and the process proceeded in the low-pressure region under the present conditions. The second-order rate constant was expressed as k /Ar = 10 14,74 exp(−35.2 kcal mol −1 / RT ) cm 3 mol −1 s −1 . Applying the RRKM strong collision theory, the value of the threshold energy and the collision efficiency were discussed.

Thermal decomposition of ethyl acetate. Branching ratio of the competing paths in the pyrolysis of the produced acetic acid

Abstract The thermal decomposition of ethyl acetate was investigated in the temperature range of 1300–1800 K using a shock tube. The initial process was a unimolecular decomposition producing equimolar ethylene and acetic acid. In the higher temperature range acetic acid decomposed consecutively through the following reaction paths: CH 3 COOH→CH 2 CO+H 2 O and CH 3 COOH→CH 4 +CO 2 . At low densities the yield of the products from the latter reaction decreased in comparison with that of normal acetic acid. This tendency was opposite to that for formic acid produced from ethyl formate.