Chemical Physics Letters (v.436, #4-6)

Contents (iii-viii).

Far infrared stimulated emission from the 8s and 8f Rydberg states of NO by Y. Ogi; J. Ando; M. Nemoto; M. Fujii; K. Tono; K. Tsukiyama (303-307).
Stimulated emission of NO in the far infrared region has been analyzed. The longest wavelength detected in the current study is ∼27 μm (∼11 THz), which is corresponding to the 8sσ → 7pσ inter-Rydberg transition. The possibility of the black body induced transitions is briefly discussed.Directional light emission of NO in the far infrared region has been analyzed. Two main stimulated emission channels around 27 μm (≈11 THz) and 14 μm for the 8sσ2Σ+(v  = 0) level have been identified as the 8sσ → 7pσ and 8sσ → 6f transitions, respectively. Two dominant band systems around 19 and 21 μm for the 8f(v  = 0) complex have been assigned to the 8f → 7g and 8f → 7dσ transitions, respectively. The possibility of the black body induced transitions is briefly discussed.

Electron impact excitation of molecules: Calculation of the cross section using the similarity function method and ab initio data for electronic structure by S. Adamson; V. Astapenko; M. Deminskii; A. Eletskii; B. Potapkin; L. Sukhanov; A. Zaitsevskii (308-313).
The electron impact excitation cross section of dipole-allowed transitions of diatomic molecules has been evaluated using the similarity function method combined with ab initio electronic structure calculations. In accordance with the similarity function method the excitation cross section is expressed through the oscillator strength of the transition and some universal function of the reduced incident electron energy. The necessary characteristics of molecular terms involved are determined through ab initio electronic structure calculations using the multireference configuration interaction technique or relativistic multipartitioning many-body perturbation theory. Comparison of results of specific calculations performed for CO and NO with available experimental data and comprehensive quantum-mechanical calculations shows a reasonable agreement.Electron impact excitation cross sections of dipole-allowed transitions in diatomic molecules have been evaluated using the similarity function method allowing one to express cross sections through the oscillator strength of the transition and some universal function of the reduced incident electron energy. The necessary characteristics of the molecular terms involved and transition dipoles were determined by ab initio electronic structure calculations using the multireference configuration interaction technique or relativistic multipartitioning many-body perturbation theory. The results of specific calculations performed for CO and NO in a reasonable agreement with the available experimental data and the results of comprehensive quantum-mechanical calculations.

The tautomerization dynamics of porphycene and its isotopomers – Concerted versus stepwise mechanisms by Z. Smedarchina; M.F. Shibl; O. Kühn; A. Fernández-Ramos (314-321).
The tautomerization of porphycene, which can be a concerted or a stepwise process, is studied by density-functional theory and instanton techniques. The zero-level tunneling splitting and tautomerization rate constants are calculated, and compared with gas-phase and NMR measurements, respectively. An apparent discrepancy between the two sets of experimental data are revealed and discussed.To determine whether the tautomerization of porphycene is a concerted or a stepwise process, we characterize its stationary points on the potential energy surface employing density functional theory as well as Møller–Plesset perturbation theory, and calculate proton-transfer rates and the zero-level tunneling splitting using the approximate instanton method. The results are compared with experimental rate constants and activation energies measured in solid state by NMR techniques, and with the zero-level tunneling splitting measured in gas phase. An apparent discrepancy between the two sets of experimental data emerges from this comparison, which is reassessed in terms of general relations that are independent of the quality of the calculated potentials. We show how kinetic isotope effects can be used to distinguish the two mechanisms experimentally.

Interaction components in the hydrogen halide dications by P. Candori; S. Falcinelli; F. Pirani; F. Tarantelli; F. Vecchiocattivi (322-326).
The interatomic interaction in HX2+ dications (X = halogen atom) have been studied by a semiempirical method and ab initio calculations.We have theoretically investigated the interatomic interaction in the low-lying states of HX2+ dications (X = F, Cl, Br, I) by combining results from semiempirical method with ab initio calculations. Main targets have been the complete characterization of the dependence of the charge transfer on the internuclear distance and on the nature of X atom, together with the assessment of its role with respect to other interaction components. The present analysis accounts for differences in the experimental findings related to the features of the permitted bound levels, which are lacking in HF2+ and increase in number and stability on going towards HI2+.

Vibrational satellites of dipole-forbidden transitions in Xe/CF4 mixtures by Vadim A. Alekseev; Nikolaus Schwentner (327-330).
Long range combination of dipole allowed molecular vibration and forbidden atomic states yields strong satellites near resonance transitions.Absorption and fluorescence excitation spectra of Xe/CF4 mixtures display numerous spectrally narrow bands coinciding with energies of the np- and nd-states of the Xe atom increased by the energy of one ν 3-quantum (ν 3  = 1281 cm−1) of CF4.

Velocity distribution of the pulsed ND3 molecular beam selected by a quadrupole Stark velocity filter by Hidenobu Tsuji; Yasumasa Okuda; Takao Sekiguchi; Hideto Kanamori (331-334).
Slow ND3 molecules are selected from Maxwell–Boltzmann distribution at room temperature by using a pulsed nozzle and a Stark filter. The velocity distribution after the filter is derived (dots) from TOF measurement, and agrees well with a simulation based on Stark effects on all the rotational states (red). For example, the contribution from a single rotational state is shown (blue). The slowest component detected is equivalent to T  = 4 K of the thermal energy.We selected the slow velocity components from the ND3 molecules with Maxwell–Boltzmann distribution at room temperature by using a pulsed nozzle and a quadrupole Stark guide. The velocity distribution after the filtering system shows good agreement with theory based on the Stark energy shift in molecular rotational states. We can detect the component of 60 m/s as the slowest column, which corresponds to 4 K of the thermal energy. This result promises that molecules in the mK region would be obtainable by combining this technique with a pre-cooling process like He buffer gas cooling.

Infrared absorption spectra of SO2 clusters in supersonic jet observed by cavity ring-down spectroscopy. A pressure-dependence of the spectra and contour analysis led us to the first identification of SO2 dimer in gas phase.We have observed infrared spectra of the SO2 clusters in gas phase for the first time by cavity ring-down spectroscopy, and assigned absorption bands of dimer and larger clusters in the O=S=O asymmetric stretching region. An analysis of the rotational contour showed that the dimeric band can be assigned to the SO2 vibration in an electron-donor side of the Cs-isomer of (SO2)2 observed by Fourier-transform microwave spectroscopy [A. Taleb-Bendiab et al., J. Chem. Phys. 94 (1991) 6956.]. The observed band type and wavenumber shift from monomer was consistent with the results of quantum chemical calculations.

Photoelectron spectra of FeS explained by a CASPT2 ab initio study by Sergiu Clima; Marc F.A. Hendrickx (341-345).
A CASPT2 study of the FeS-spectra is presented. The spectral features can be viewed as a result of one electron removal from one of these orbitals.Potential energy curves for the ground states for FeS and FeS, and of several low-lying electronic states that are responsible for the FeS photoelectron spectrum, are calculated at the CASPT2 level. Our computational approach predicts a dissociation energy D 0  = 3.13 eV and an FeS electron affinity of 1.70 eV. The ground state of FeS is 5Σ+, in agreement with a previous CASSCF/ACPF study but in disagreement with a very recent investigation of the microwave spectrum. New assignments of the photoelectron spectrum of FeS are presented.

DFT studies of gas-phase reaction mechanism of coordinatively unsaturated W(CO)5 with NO by Yo-ichi Ishikawa; Kenta Kawakami; Hiroshi Teraguchi; Hirotaka Nakazawa (346-351).
The DFT calculations suggested that, in the gas phase coordination of NO to W(CO)5, a simple coordination to form W(CO)5(NO) did not occur but the following sequential concerted reactions occur: W(CO)5  + NO → [W(CO)5(NO) (–CO)] → W(CO)4(NO)(+NO) →  [W(CO)4(NO)2 (−CO)] → W(CO)3(NO)2.The reaction of coordinatively unsaturated W(CO)5 with NO is investigated using density functional theory. B3LYP-based calculations with ECPs (LANL2DZ) on W and 6-311+G(2d) all-electron basis sets on C, N, and O are used to characterize transients observed in the vibrational absorption spectra of CO and NO ligands observed by a time-resolved infrared absorption spectroscopy after the 355-nm pulse laser photolysis of W(CO)6/NO/Ar mixture [Y. Ishikawa and S. Arai, Chem. Phys. Lett. 253 (1996) 230]. The calculations suggested that, in the gas phase reaction of NO with W(CO)5, simple coordination to form W(CO)5(NO) does not occur but, instead, sequential concerted displacement of CO takes place to form W(CO)3(NO)2.

We have calculated the energy for neutral atoms and cations with 3 ⩽ Z ⩽ 36 with explicitly correlated wave functions including near degeneracy effects by using variational Monte Carlo.The ground state of the cations Li+ through Kr+ has been studied by using explicitly correlated wave functions. The variational wave function has been previously used [E. Buendía, F.J. Gálvez, A. Sarsa, Chem. Phys. Lett. 428 (2006) 241] to study the corresponding neutral atoms. Near degeneracy has been also considered by means of a multi-configurational model wave function for a number of neutral atoms and cations. Starting from the total energy of the cations here obtained along with previously reported neutral atom energies (except for some cases here discussed), the ionization potential of these atoms has been calculated by including relativistic effects perturbatively. The calculation has been carried out by using the variational Monte Carlo method.

6-Hydroxyquinoline (6-HQ) in benzene emits normal fluorescence around 357 nm. In the presence of acetic acid (HOAc), it exhibits two more bands at ∼419 nm and a large Stokes shifted one at ∼583 nm with decreased intensity of the normal fluorescence. It appears to form (1:1) and (1:2) complexes-(1:2) 6-HQ/HOAc undergoes an excited state proton rearrangement (via HOAc wire) resulting in keto tautomer (emitting at ∼583 nm). This appears to be in line with recent findings where ammonia wires facilitate proton/hydrogen translocation (Science, 302, 1736, 2003). However, (1:1) 6-HQ/HOAc exhibits intermediate emission (∼419 nm) presumably due to ESIPT.6-Hydroxyquinoline (6-HQ) in benzene emits normal fluorescence around 357 nm. In the presence of acetic acid (HOAc), it exhibits two more bands at ∼419 nm and a large Stokes shifted one at ∼583 nm with decreased intensity of the normal fluorescence. It appears to form (1:1) and (1:2) complexes-(1:2) 6-HQ/HOAc undergoes an excited state proton rearrangement (via HOAc wire) resulting in keto tautomer (emitting at ∼583 nm). This appears to be in line with recent findings where ammonia wires facilitate proton/hydrogen translocation (Science, 302, 1736, 2003). However, (1:1) 6-HQ/HOAc exhibits intermediate emission (∼419 nm) presumably due to ESIPT.

Computational study of anion solvation in nitrobenzene by Elvis S. Böes; Jones de Andrade; Hubert Stassen; Paulo F.B. Gonçalves (362-367).
The PCM was parameterized for anion solvation in nitrobenzene for a set of 22 anions containing the important chemical functionalities.The solvation of anions in nitrobenzene was investigated by the polarizable continuum model (PCM). The PCM was parameterized from structural information obtained by molecular dynamics simulations (MD) of anionic solutions in nitrobenzene. The parameterization was performed against experimental free energies of solvation for 22 anions containing H, C, N, O, F, S, Cl, Br, Se, and I atoms. The calculated Gibbs free energies of solvation present a mean absolute deviation from the experimental data of 2.4 kcal/mol. Hartree–Fock and DFT computations produce equivalent results.

Decorating carbon nanotubes with nickel nanoparticles by C. Bittencourt; A. Felten; J. Ghijsen; J.J. Pireaux; W. Drube; R. Erni; G. Van Tendeloo (368-372).
Carbon nanotubes were decorated with Ni clusters by thermal evaporation. It is shown that the CNT decoration with Ni varies from well-organized clusters to the complete coverage of the surface resulting in electronic charge transfer and formation of Ni–C bonds at the interface between these.Carbon nanotubes (CNTs) were decorated with Ni clusters by thermal evaporation. It is shown that the CNT decoration with Ni varies from well-organized clusters to the complete coverage of the surface resulting in electronic charge transfer and formation of Ni–C bonds at the interface between these two materials, depending on the evaporated amount of Ni. The Ni–CNTs interaction induces an increase in the metallicity of the system suggesting that CNTs decorated with metal atoms can be a good candidate as template for production of metal nanowires.

EPR study on paramagnetic species in nitrogen-doped ZnO powders prepared by a mechanochemical method by Shinya Moribe; Tadaaki Ikoma; Kimio Akiyama; Qiwu Zhang; Fumio Saito; Shozo Tero-Kubota (373-377).
Nitrogen-doped ZnO (N-ZnO) powders prepared by a mechanochemical method show two kinds of EPR signals due to a singly ionized nitrogen ( N 2 - ) and a shallow donor. Visible light irradiation of the N-ZnO particles reveals a reversible response of reduction of the EPR signal of the N 2 - radical site and an increase due to a shallow donor.Paramagnetic species in nitrogen-doped ZnO (N-ZnO) powders, visible light sensitive photocatalysts exhibiting antibacterial activity, have been investigated using EPR spectroscopy. The N-ZnO photocatalysts showed two kinds of EPR signals due to a singly ionized nitrogen ( N 2 - ) and a shallow donor. Visible light irradiation to the N-ZnO particles shows reversible response of reduction of EPR signal of the N 2 - radical site and increase of that due to shallow donor. The results indicate that the N 2 - is converted to a diamagnetic neutral molecular nitrogen acceptor ( N 2 0 ) by visible light and photoinduced electrons are trapped to the shallow donor sites.

Alignment of vapor-grown carbon fibers in polymer under magnetic field by Tatsuhiro Takahashi; Kazuhito Suzuki; Hiroshi Awano; Koichiro Yonetake (378-382).
Magnetic field (0.23 T) was applied to the dispersion of vapor-grown carbon fibers, having averaged diameter of 150 nm with averaged length of 3.9 μm, in polydimethylsiloxane (0.097 Pa s) during in situ optical microscope observation with high magnification. The alignment rate was determined by measuring rotational angles as a function of time.A trace amount of vapor-grown carbon fibers (VGCFs) were dispersed in polydimethylsiloxane (0.097 Pa s) by mechanical stirring. A magnetic field (0.23 T) was applied to the dispersion while in situ optical microscope observation was performed. The alignment rate was determined through analysis of the VGCF orientation. Using this suspension method, the diamagnetic anisotropic susceptibility of VGCF was estimated to be 3.11 × 10−4 (–). From this value, the alignment time of VGCFs was estimated as a function of viscosity or magnetic field. The anisotropic susceptibility of VGCFs was compared with those of conventional carbon fibers.

Application of Jarzynski’s equality in simple versus complex systems by Turgut Baştuğ; Serdar Kuyucak (383-387).
Lateral views of the carbon nanotube (left) and the gramicidin A channel (right) systems. The nanotube is surrounded by a layer of capped nanotubes (only two are shown for clarity). Gramicidin A is embedded in a lipid bilayer (only the head groups of the lipid molecules are depicted by large balls). The K+ ion is at the pore centre surrounded by single-file water molecules (little balls) in both cases. The systems are hydrated with water on both sides.Jarzynski’s equality provides a non-equilibrium method for calculation of free energies, which could have wide-ranging applications in complex molecules. Tests of Jarzynski’s equality have mostly focused on simple systems or near-equilibrium processes. Here we present a benchmark test that compares the results of free energy calculations for a potassium ion in carbon nanotube and gramicidin channel, which can be identified with simple and complex systems. A good agreement is found between the free energy results obtained using Jarzynski’s equality and established methods in the carbon nanotube, but discrepancies occur in gramicidin, indicating relaxation problems in application of Jarzynski’s equality to complex biomolecular processes.

A joined theoretical–experimental investigation on the 1H and 13C NMR chemical shifts of chloro-alkenes by Philippe d’Antuono; Edith Botek; Benoît Champagne; Joris Wieme; Marie-Françoise Reyniers; Guy B. Marin; Peter J. Adriaensens; Jan M. Gelan (388-393).
Interpretation of NMR spectra of PVC chains containing unsaturations is facilitated by DFT calculationsThe 1H and 13C NMR chemical shifts of model chloro-alkenes are evaluated at different levels of approximation and compared to experimental data. DFT calculations employing the B3LYP exchange-correlation functional with the 6-311+G(2d,p) basis turned out to be reliable to account for most of the variations of the chemical shifts. Then, after accounting for the linear regression fits, the mean absolute error goes down to 3.8 ppm and 0.05 ppm for the 13C and 1H chemical shifts, respectively. Using these linear regression relationships, the NMR chemical shifts are determined for a PVC chain bearing an unsaturated defect inside a meso and a racemic dyad. These simulations, which account for the many conformations of the PVC segment, are used to interpret recent experimental spectra of PVC containing unsaturations.

Our reparametrized meta-GGA exchange-correlation functional was designed to improve the performances for hydrogen-bonded and van der Waals complexes.A new density functional combining the TPSS meta-GGA exchange and the τ1 meta-GGA correlation is studied. The parameters in the τ1 meta-GGA correlation model are reoptimized in a synchronized way to match the original TPSS meta-GGA exchange functional. This reparametrized meta-GGA exchange-correlation functional, named TPSSτ3, yields improved results for hydrogen-bonded and van der Waals complexes compared to Bmτ1 and TPSSτ1.

Author Index (401-408).