Dissociation of benzene dication [C6H6]2+: exploring the potential energy surface

The singlet potential energy surface for the dissociation of benzene dication has been explored, and its three major dissociation channels have been studied: C6H6(2+) --> C3H3(+) + C3H3(+), C4H3(+) + C2H3(+), and C5H3(+) + CH3(+). The calculated energetics suggest that the products will be formed with considerable translational energy because of the Coulomb repulsion between the charged fragments. The calculated energy release in the three channels shows a qualitative agreement with the experimentally observed kinetic energy release. The formation of certain intermediates is found to be common to the three dissociation channels.     

Metastable decomposition and hydrogen migration of ethane dication produced in an intense femtosecond near-infrared laser field

We investigated a formation channel of triatomic molecular hydrogen ions from ethane dication induced by irradiation of intense laser fields (800 nm, 100 fs, ～1 × 10(14) W∕cm(2)) by using time of flight mass spectrometry. Hydrogen ion and molecular hydrogen ion (H,D)(n)(+) (n = 1-3) ejected from ethane dications, produced by double ionization of three types of samples, CH(3)CH(3), CD(3)CD(3), and CH(3)CD(3), were measured. All fragments were found to comprise components with a kinetic energy of ～3.5 eV originating from a two-body Coulomb explosion of ethane dications. Based on the signal intensities and the anisotropy of the ejection direction with respect to the laser polarization direction, the branching ratios, H(+):D(+) = 66:34, H(2)(+):HD(+):D(2)(+) = 63:6:31, and H(3)(+):H(2)D(+):HD(2)(+):D(3)(+) = 26:31:34:9 for the decomposition of C(2)H(3)D(3)(2+), were determined. The ratio of hydrogen molecules, H(2):HD:D(2) = 31:48:21, was also estimated from the signal intensities of the counter ion C(2)(H,D)(4)(2+). The similarity in the extent of H∕D mixture in (H,D)(3)(+) with that of (H,D)(2) suggests that these two dissociation channels have a common precursor with the C(2)H(4)(2+)...H(2) complex structure, as proposed theoretically in the case of H(3)(+) ejection from allene dication [A. M. Mebel and A. D. Bandrauk, J. Chem. Phys. 129, 224311 (2008)]. In contrast, the (H,D)(2)(+) ejection path with a lower extent of H∕D mixture and a large anisotropy is expected to proceed essentially via a different path with a much rapid decomposition rate. For the Coulomb explosion path of C-C bond breaking, the yield ratios of two channels, CH(3)CD(3)(2+)→ CH(3)(+) + CD(3)(+) and CH(2)D(+) + CHD(2)(+), were 81:19 and 92:8 for the perpendicular and parallel directions, respectively. This indicates that the process occurs at a rapid rate, which is comparable to hydrogen migration through the C-C bond, resulting in smaller anisotropy for the latter channel that needs H∕D exchange.     

Application of discrete variable representation to planar H(2) (+) in strong xuv laser fields

We present an efficient and accurate grid method to study the strong field dynamics of planar H(2) (+) under Born-Oppenheimer approximation. After introducing the elliptical coordinates to the planar H(2) (+), we show that the Coulomb singularities at the nuclei can be successfully overcome so that both bound and continuum states can be accurately calculated by the method of separation of variables. The time-dependent Schro?dinger equation (TDSE) can be accurately solved by a two-dimensional discrete variable representation (DVR) method, where the radial coordinate is discretized with the finite-element discrete variable representation for easy parallel computation and the angular coordinate with the trigonometric DVR which can describe the periodicity in this direction. The bound states energies can be accurately calculated by the imaginary time propagation of TDSE, which agree very well with those computed by the separation of variables. We apply the TDSE to study the ionization dynamics of the planar H(2) (+) by short extreme ultra-violet (xuv) pulses, in which case the differential momentum distributions from both the length and the velocity gauge agree very well with those calculated by the lowest order perturbation theory.     

Templated synthesis of the novel layered silver-antimony sulfides [H3NCH2CH2NH2][Ag2SbS3 and [H3NCH2CH2NH2]2[Ag5Sb3S8

Two new silver-antimony sulfides, [C(2)H(9)N(2)][Ag(2)SbS(3)] (1) and [C(2)H(9)N(2)](2)[Ag(5)Sb(3)S(8)] (2), have been prepared solvothermally in the presence of ethylenediamine and characterized by single-crystal X-ray diffraction, thermogravimetry, and elemental analysis. Compound 1 crystallizes in the space group Pn (a = 6.1781(1) A, b =11.9491(3) A, c = 6.9239(2) A, beta =111.164(1) degrees ) and 2 in the space group Pm (a = 6.2215(2) A, b = 15.7707(7) A, c = 11.6478(5) A, beta = 92.645(2) degrees ). The structure of 1 consists of chains of fused five-membered Ag(2)SbS(2) rings linked to form layers, between which the template molecules reside. Compound 2 contains honeycomb-like sheets of fused silver-antimony-sulfide six-membered rings linked to form double layers. The idealized structure can be considered to be an ordered defect derivative of that of lithium bismuthide, Li(3)Bi, and represents a new solid-state structure type.     

Infrared-vacuum ultraviolet pulsed field ionization-photoelectron study of C2H4(+) using a high-resolution infrared laser

The infrared (IR)-vacuum ultraviolet (VUV)-pulsed field ionization-photoelectron (IR-VUV-PFI-PE) spectrum for C2H4(X1A(g), v11 = 1, N'(Ka'Kc') = 3(03)) in the VUV range of 83,000-84,800 cm(-1) obtained using a single mode infrared laser revealed 24 rotationally resolved vibrational bands for the ion C2H4(+)(X2B(3u)) ground state. The frequencies and symmetry of the vibrational bands thus determined, together with the anharmonic frequency predictions calculated at the CCSD(T)/aug-cc-pVQZ level, have allowed the unambiguous assignment of these vibrational bands. These bands are mostly combination bands. The measured frequencies of these bands yield the fundamental frequencies for v8+ = 1103 +/- 10 cm(-1) and v10+ = 813 +/- 10 cm(-1) of C2H4(+)(X2B(3u)), which have not been determined previously. The present IR-VUV-PFI-PE study also provides truly rovibrationally selected and resolved state-to-state cross sections for the photoionization transitions C2H4(X1A(g); v11, N'(Ka'Kc')) --> C2H4(+)(X2B(3u); vi+, N+(Ka+Kc+)), where N'(Ka'Kc') denotes the rotational level of C2H4(X1A(g); v11), and vi+ and N+(Ka+Kc+) represent the vibrational and rotational states of the cation.     

Butterfly C2H2++: new way for the decomposition of the acetylene dication

Using highly correlated ab initio methods, a new transition state is characterized in the lowest singlet potential energy surface of HCCH(++). This transition state possesses a dibridged (or "butterfly") form not observed yet for any acetylic compound. It can be reached either directly or after spin-orbit conversion of triplet HCCH(++) ions. In light of these calculations, a reaction pathway for the proton pair formation (i.e., HCCH(++)-->C(2)+H(+)+H(+)) is proposed.     

Dissociation and rearrangements of the molecular ions of sulfides,sulfoxides, and sulfones generated by a strong electric field

The field mass spectra of 18 sulfides, sulfoxides, and sulfones were investigated, and the principles of charge localization in the dissociation and rearrangements of the molecular ions of these compounds were established. A new type of fragmentation leading to the elimination of S^+., SO^+., and SO₂. was observed. A new mechanism, according to which cleavage of two C-S bonds and the formation of one new C-C bond due to radical recombination cocur in the cyclic transition complex, is proposed. Prior migration of alkyl radicals from sulfur to oxygen with subsequent cleavage of the S-O and C-S bonds via the above-mentioned mechanism may also occur in the molecular ions of sulfoxides and sulfones.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 2, pp. 172–181, March–April, 1987.     

ZnO Nanocluster as a Potential Catalyst for Dissociation of H2S Molecule

Adsorption of hydrogen sulfide (H₂S) on the external and internal surface of Zn₁₂O₁₂ nanocluster was studied by using density functional calculations. The results indicate that the H₂S molecule is physically adsorbed or chemically dissociated by the nanocluster. It was found that the H₂S molecule can dissociate into –H and–SH fragments, suggesting that the nanocluster might be a potential catalyst for dissociation of the H₂S molecule. Also, dissociation of H₂S to S species in internal surface of the Zn₁₂O₁₂ nanocluster is energetically impossible. The HOMO–LUMO energy gap of H₂S dissociation configuration is changed about 27.68 %, indicating that the electronic properties of the nanocluster by dissociation process have strongly changed.     

Hypervalent organobismuth(iii) carbonate, chalcogenides and halides with the pendant arm ligands 2-(Me2NCH2)C6H4 and 2,6-(Me2NCH2)2C6H3

R2BiOH (1) [R = 2-(Me2NCH2)C6H4] and (R2Bi)2O (2) are formed by hydrolysis of R2BiCl with KOH. Single crystals of were obtained by air oxidation of (R2Bi)2. The reaction of R2BiCl and Na2CO3 leads to (R2Bi)2CO3 (3). 3 is also formed by the absorption of CO2 from the air in solutions of 1 or 2 in diethyl ether or toluene. (R2Bi)2S (4) is obtained from R2BiCl and Na2S or from (R2Bi)2 and S8. Exchange reactions between R2BiCl and KBr or NaI give R2BiX [X = Br (5), I (6)]. The reaction of RBiCl2 (7) with Na2S and [W(CO)5(THF)] gives cyclo-(RBiS)2[W(CO)5]2 (8). cyclo-(R'BiS)2 (9) [R' = 2,6-(Me2NCH2)2C6H3] is formed by reaction of R'BiCl2 and Na2S. The structures of were determined by single-crystal X-ray diffraction.     

Application of parametric equations of motion to study the laser induced multiphoton dissociation of H2+ in intense laser field

We have applied parametric equations of motion (PEM) to study photodissociation dynamics of H(2)(+). The resonances are extracted using smooth exterior scaling method. This is the first application of PEM to non-Hermitian Hamiltonian that includes resonances and the continuum. Here, we have studied how the different resonance states behave with respect to the change in field amplitude. The advantage of this method is that one can easily trace the different states that are changing as the field parameter changes.     

Decomposition of hexafluoropropylene oxide in a strong IR field

Multiphoton dissociation (MPD) of hexafluoropropylene oxide (HFPO) under focused CO₂-laser radiation was studied. A high-energy channel of HFPO decomposition was revealed. The dependences of the MPD yield and the ratio between various channels of HFPO decomposition on the laser radiation frequency in the range from 967.7 to 1090.0 cm^–1, the incident radiation energy, and the initial pressure of HFPO were obtained. A considerable contribution of thermal decomposition of HFPO occurring outside of the irradiated zone to the total yield of its decomposition was established. An explanation for the pressure dependence of the yield of HFPO decomposition was suggested.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2174–2180, November, 1995.The authors are grateful to the Russian Foundation for Basic Research for financial support of this work (Project No. 94-03-09059).     

Application of the finite element method to time-dependent quantum mechanics: II. H 2 + in a laser field

A finite element method in Cartesian coordinates in three dimensions is described to solve the time-dependent Schrödinger equation for H ₂ ⁺ in the presence of time-dependent electromagnetic fields. The ionization rates, nonlinear optical polarizabilities and harmonic generation spectrum of H ₂ ⁺ have been calculated for field directions parallel or perpendicular to the hydrogen molecule ion axis. Comparisons of the present numerical results with previously published calculations show that the finite element method reproduces perturbative results and can treat nonperturbativity arbitrary intense short pulses as it includes automatically both bound and continuum electronic states.