Ginji Fujisawa

Translational energy distributions of the products of the 193 and 157 nm photodissociation of chloroethylenes

The 193 and 157 nm photodissociations of three isomers of dichloroethylene (DCE) and trichloroethylene (TCE) were investigated using a technique of photofragmentation translational spectroscopy. The photofragmentation mechanisms were constructed by analyzing the time-of-flight spectra of C2H2+, Cl+, HCl+, C2HCl+, and C2Cl2+ produced by electron impact of neutral photofragments. In the 193 nm photodissociation, both the HCl elimination and the C–Cl bond rupture were important for all the compounds examined. It was concluded that secondary dissociation of the vibrationally excited chlorinated vinyl radical produced by the C–Cl bond rupture was important even at 193 nm. In the 157 nm photodissociation, the mechanisms were similar to those at 193 nm for cis-DCE, 1,1-DCE, and TCE, while only the C–Cl bond rupture occurred for trans-DCE. This result suggests that the 157 nm photodissociation of trans-DCE proceeds via the direct photodissociation following the photoexcitation to the repulsive 1nσ* state. A minor...

The mechanism of the unimolecular dissociation of trichloroethylene CHCl=CCl2 in the ground electronic state

The unimolecular dissociation of trichloroethylene in its electronic ground state has been investigated using an infrared multiphoton dissociation combined with photofragmentation translational spectroscopy to measure product translational energies. The main reaction channel was found to be HCl elimination on the basis of observed product time‐of‐flight (TOF) spectra. A center‐of‐mass translational energy distribution for this channel provides direct evidence for competition between two channels, three‐ and four‐centered HCl eliminations. Cl elimination was found to be a minor but significant channel from observed Cl+ and C2HCl+TOF spectra. The branching ratios were determined as 0.28, 0.55, and 0.17 for the three‐ and four‐centered HCl eliminations and the Cl elimination, respectively. The three‐centered channel exhibits a ‘‘statistical’’ translational energy distribution which is typical for a reaction with no potential energy barrier in the reverse reaction, that is to say, no exit barrier reaction. In...

Infrared multiphoton dissociation of 2‐chloro‐1,1,1,2‐tetrafluoroethane in a molecular beam

Mechanism and dynamics of the infrared multiphoton dissociation of 2‐chloro‐1, 1,1,2‐tetrafluoroethane have been studied using a photofragmentation translational spectroscopy. The molecule dissociates competitively through three‐centered elimination of HCl and C–Cl bond rupture. The HCl elimination reaction accounts for 74% of the total primary dissociation yields. The center‐of‐mass translational energy distribution for the HCl elimination indicates that an exit barrier of several kcal/mol exists along the reaction coordinate on the potential energy surface. The infrared multiphoton dissociation of CF3CF produced by the HCl elimination from CF3CHClF also occurs as a secondary process through its dissociation into two CF2 molecules. The average excitation energy of dissociating CF3CHClF has been determined to be about 20 kcal/mol above the C–Cl dissociation threshold of the molecule by comparing the observed center‐of‐mass translational energy distribution for the C–Cl bond rupture reaction with that calc...

Molecular beam study on infrared multiphoton dissociation of octafluorocyclobutane

Abstract Unimolecular dissociation dynamics of octafluorocyclobutane has been studied using photofragmentation translational spectroscopy. The product translational energy distribution for the reaction cyclo-C4F8 → 2 C2F4 peaks at 31 kJ/mol with an average of 40 kJ/mol, which amounts to about 30% of the exit channel barrier. The energy partitioning to the relative translation of the products and dynamics of the dissociation have been discussed on the basis of the impulsive models with help of transition state structures calculated using an ab initio molecular orbital method.

Excitation Profile of the Resonance Raman Effect of Uranyl Nitrate in Dimethyl Sulfoxide

The resonance Raman spectra of uranyl nitrate in dimethyl sulfoxide (DMSO) were measured at room temperature, with the use of ten output lines (528.7, 514.5, 501.7, 496.5, 488.0, 476.5, 472.7, 465.8, 457.9, and 454.5 nm) of an argon-ion laser. The excitation profile of the resonance Raman effect has been obtained by plotting the relative intensities of the uranyl symmetric stretching vibration at 835 cm−1 against the laser exciting wavelengths. It has been found that the observed excitation profile of the uranyl symmetric stretching vibration resembles the vibronic structure of the electronic absorption spectrum. Also, the excitation profile obtained is briefly discussed in relation to the theory developed by J. Tang and A. C. Albrecht.

Selective T/H separation by NH3 laser multiple-photon dissociation of CTCL3

The multiple-photon dissociation (MPD) of CTCL3 and the selectivity of T/H separation were investigated using a pulsed NH3 laser, whose radiation contained a few lines depending on operating conditions. When Xe was added to chloroform, the dissociation rate of CTCL3 increased at chloroform pressures below 2 Torr as a consequence of the removal of multiple-photon absorption bottleneck by collisions with Xe. The dissociation rate of CTCl3 decreased monotonically with increasing chloroform pressure from 0.2 to 7 Torr. The depletion of CHCl3 was not observed within experimental errors. The lower limit of the tritium enrichment factor in photo-products produced by one pulse irradiation was 570 at chloroform pressure of 2 Torr.

Infrared multiphoton dissociation of 1,1-dichloroethene

Abstract The relative translational energy of distribution of HCl and C 2 HCl formed in the infrared multiphoton dissociation of 1,1-dichloroethene was measured by the time-of-flight method. The mean translational energy was evaluated to be 46 kJ mol −1 . The distribution estimated in this study was close to that estimated in the 193 nm photodissociation. The rate constants for the HCl elimination and 1,1–1,2 isomerization were calculated by employing RRKM theory on the basis of an ab initio potential surface. A model for the dissociation which includes the migration processes of H and Cl atoms was proposed to interpret the present and previous experimental results.

Tritium separation by laser multiple-photon dissociation of CDTCl2/CD2Cl2 mixture

Abstract Selective multiple-photon dissociation of CDTCl 2 in CD 2 Cl 2 was studied using a TEA CO 2 laser. The dissociation rate of CDTCl 2 had a maximum value at 927 cm −1 (P (38) line) irradiation. The frequency agreed with the calculated ν 7 vibrational frequency (929 cm −1 ) of CDTCl 2 within the accuracy of the calculation. The tritium enrichment factor β prod was obtained to be 29 −15 +156 at 3 Torr total pressure and at 907.8 cm −1 irradiation.

Preferential C–Cl bond rupture from 1‐bromo‐2‐chloro‐1,1,2‐trifluoroethane following photoabsorption via n(Cl)→σ*(C–Cl) transition

The photodissociation mechanism and dynamics of the title molecule have been studied at excitation wavelengths of 157 and 193 nm by using a photofragmentation translational spectroscopy. In the case of the excitation at 157 nm, the C–Cl and C–Br bond ruptures occur competitively with the branching ratio of 1.0:0.3, indicating the preferential C–Cl bond rupture over the weaker C–Br bond. The C–Br bond rupture occurred via two pathways; the dissociation on the excited repulsive potential energy surface and the dissociation of the vibrationally excited molecule in the ground electronic state following the internal conversion. In the case of 193 nm, only the C–Br bond rupture on the repulsive potential energy surface was observed.

INFRARED MULTIPHOTON DISSOCIATION OF CBRF2CHCLF, CBRF2CHBRF, AND CBRCLFCBRF2 IN A MOLECULAR BEAM

Dynamics and mechanisms of infrared multiphoton dissociation of CBrF2CHClF, CBrF2CHBrF, and CBrClFCBrF2 have been studied using a photofragmentation translational spectroscopy. All molecules dissociated through C–Br bond rupture reactions. At high laser fluence, the halogenated ethyl radicals produced by the primary dissociation reactions dissociated through carbon–halogen bond ruptures. Center‐of‐mass product translational energy distributions for the C–Br and C–Cl bond ruptures of all halogenated ethanes and ethyl radicals studied are essentially consistent with those calculated by Rice–Ramsperger–Kassel–Marcus (RRKM) theory. This indicates that there exists essentially no exit channel barrier on the potential energy surface for the C–Br or C–Cl bond rupture of the halogenated ethanes and ethyl radicals.