Kr Dimers Research Articles

Concentration of dimers for BCl<sub>3</sub> and rare gas atoms in BCl<sub>3</sub> isotope separation

In the low temperature environment generated by supersonic flow in the process of laser assisted retardation of condensation of isotope separation for BCl<sub>3</sub>, the molecular isotopes BCl<sub>3</sub> and carrier gas (rare gas (RG): He, Ne, Ar, Kr, Xe) can form BCl<sub>3</sub>:RG dimer via contact collision process. The mechanism and relationship between dimer concentration and absolute temperature of dimer involving BCl<sub>3</sub> molecules are of great significance for regulating and selecting the isotope separation parameters. In this work, based on the analytic description of the anharmonic interaction potential function of BCl<sub>3</sub>:RG, and considering the two-body and three-body collision induced association and dissociation of dimers, the concentration of BCl<sub>3</sub>:RG dimers is obtained at the absolute temperature in a range of 20–40 K. The obtained results are as follows. The two-body collision is dominant in the formation of dimer in the low temperature range. When the initial molar fraction of BCl<sub>3</sub> is in a range of 0.01–0.10, the BCl<sub>3</sub>:RG dimer concentration changes approximately linearly with the initial molar fraction of BCl<sub>3</sub>, indicating that the initial molar fraction not only determines the theoretical upper limit of the dimer concentration, but also dominates the dimer concentration in a low temperature range. When the temperature of the supersonic flow chamber is about 20 K, the concentration of BCl<sub>3</sub>:Kr dimers is largest, and the concentrations of other dimers are also presented. Furthermore, we explain the mechanism of laser assisted retardation of condensation in separation of isotopes by using a simple model on a molecular scale by adjusting the parameters of dissociation energy and stretching vibration frequency of the dimer.

Insights into the spurious long-range nature of local r-dependent non-local exchange-correlation kernels.

A systematic route to go beyond the exact exchange plus random phase approximation (RPA) is to include a physical exchange-correlation kernel in the adiabatic-connection fluctuation-dissipation theorem. In the previous study [D. Lu, J. Chem. Phys. 140, 18A520 (2014)], we found that non-local kernels with a screening length depending on the local Wigner-Seitz radius, rs(r), suffer an error associated with a spurious long-range repulsion in van der Waals bounded systems, which deteriorates the binding energy curve as compared to RPA. We analyze the source of the error and propose to replace rs(r) by a global, average rs in the kernel. Exemplary studies with the Corradini, del Sole, Onida, and Palummo kernel show that while this change does not affect the already outstanding performance in crystalline solids, using an average rs significantly reduces the spurious long-range tail in the exchange-correlation kernel in van der Waals bounded systems. When this method is combined with further corrections using local dielectric response theory, the binding energy of the Kr dimer is improved three times as compared to RPA.

Overtone, 2NH (ν1+ν3) spectroscopy of NH3–Ar and NH3–Kr

We have recorded between 6561 and 6671 cm–1 the spectrum of jet-cooled ammonia seeded in Ne, Ar and Kr, using continuous wave cavity ring-down spectroscopy (CW-CRDS). The equivalent absorption pathlength was around 750 m. Three bands are assigned to Π(11)←Σ(00), Π(11)←Π(10) and Δ(?)←Π(10) in the 2NH, ν1+ν3←GS transition of the ortho NH3–Ar dimer. They are rotationally analysed and a simultaneous fitting procedure, together with one far-infrared ground state band from the literature is successfully achieved. A possible Mj-dependent cooling process is reported. Only the first of these bands is observed in the ortho NH3–Kr dimer, and rotationally analysed. Individual line perturbations and anomalous line broadening effects are reported. A J-dependent vibrational predissociation lifetime with a mean value around 0.6 ns is obtained for the Π(11) sub-state in NH3–Ar and NH3–Kr. Two additional bands are assigned to NH3–Ar involving close Π upper sub-states. A group of close bands from the para dimer is identified in NH3–Ar. The energy of all observed ortho and para sub-states is extracted from the analysis. Finally, more bands are reported but their carriers could not be identified.

Evaluation of model exchange-correlation kernels in the adiabatic connection fluctuation-dissipation theorem for inhomogeneous systems.

We investigated the effect of the exchange-correlation kernels of Dobson and Wang (DW) [Phys. Rev. B 62, 10038 (2000)] and Corradini, Del Sole, Onida, and Palummo (CDOP) [Phys. Rev. B 57, 14569 (1998)] in the framework of the adiabatic connection fluctuation-dissipation theorem. The original CDOP kernel was generalized to treat inhomogeneous systems, and an efficient numerical implementation was developed. We found that both kernels improve the correlation energy in bulk silicon as compared to that evaluated from the random phase approximation (RPA). In particular, the correlation energy from the CDOP kernel is in excellent agreement with the diffusion Monte Carlo result. In the case of the Kr dimer, while the DW kernel leads to stronger binding than RPA, the CDOP kernel does the opposite. The cause of this quite different behavior of the two kernels is discussed. Our study suggests that special attention needs to be paid to describe the effective interaction at the low density regions when developing model exchange-correlation kernels.

Van der Waals Interactions for Isolated Systems Calculated Using Density Functional Theory within Plasmon-Pole Approximation

We have developed a new method of calculating the van der Waals interaction in isolated systems on the bases of the van der Waals density functional theory. This method is designed to be absolutely nonempirical, applicable to any three-dimensional isolated system and implementable into various first-principles electronic state calculation codes utilizing local density approximation (LDA). The validity of this method is tested by comparing the adiabatic potentials of an Ar dimer and a Kr dimer obtained by this method to those obtained in experiments and other theoretical studies. We find that the LDA error is largely mitigated in both equilibrium bond length and cohesive energy.

Mechanism for generating stimulated VUV emission of the Xe*Kr dimer in a dc capillary discharge

The emission spectrum of a dc capillary discharge in krypton with a small (≤0.1%) xenon impurity has been experimentally studied in the 115-850-nm range. It is shown that most of the radiation energy is concentrated in a narrow VUV spectral band adjacent to the 146.96-nm resonance line of xenon and belonging to the heteronuclear Xe*Kr molecule. The power of the narrow-band VUV radiation and its angular dependence have been measured. A conclusion is drawn that the appearance of the narrow-band VUV radiation represents amplified spontaneous emission caused by transillumination of the broad-band amplifying medium by a narrow-band "seed."

Effective emission of Xe2* and Kr2* excited by a pulsed corona discharge bounded by a dielectric barrier

Experimental time–amplitude and spectral emission curves from B(1Σ+u)−X (1Σ+g), A(3Σ+u)−X (1Σ+g) transitions in Xe2*(λ = 172 nm), Kr2* (λ = 146 nm), and Ar2* (λ =126 nm) molecules excited by a dielectric barrier bounded pulsed corona discharge are presented as a function of gas pressure, pulse repetition rate, and average excitation power. Experimentally, under optimal conditions, the Xe and Kr dimers emission efficiency were 45–50 and 25–28%, respectively.

State-of-the-art correlated ab initio potential energy curves for heavy rare gas dimers: Ar2, Kr2, and Xe2

Characteristics of the heavy rare gas dimers (Ar2,Kr2,Xe2) have been studied by correlated ab initio calculations. All-electron CCSD(T) calculations were performed for Ar and Kr dimers, and calculations with relativistic effective core potentials were performed for Kr and Xe dimers. Extended basis sets (aug-cc-pVXZ, X=D, T, Q, 5, 6) were combined with bond functions (spd, spdfg). The use of bond functions significantly improves the basis set convergence. For the argon dimer, we have included also a CCSDT correction yielding a higher quality potential energy curve. This correction has been calculated using aug-cc-pVTZ+spd basis set. All possible sources of errors have been analyzed for the argon dimer [basis set saturation, correlation contributions going beyond CCSD(T) method, effect of core corrections and relativistic corrections]. In the case of the Ar dimer, the highest level of theory reproduces the semiempirical stabilization energy within 1.3 cm−1. To obtain even closer agreement with experiment it would be necessary to fully include quadruple and higher excitations as well as to account properly for the core corrections with yet unpublished core oriented basis sets. Further improvement of one electron basis set will not lead to a better agreement with experiment. In the case of the other two dimers, the agreement between theory and experiment is also acceptable but not quantitative as in the case of the Ar dimer. Apparently, current calculations are close to the basis set limit and better agreement can only be obtained by proper covering of contributions mentioned for the argon dimer. The newly developed ECP oriented aug-cc-pVXZ basis set is very effective and can be recommended for high level calculations of molecular clusters containing heavier rare gas elements. The fast DZ/TZ extrapolation technique has been extended so that the use of empirical parameters can be avoided. Results obtained by extrapolations with medium size basis sets are surprisingly close to the most accurate ones. Further, the MP2–CCSD(T) difference was shown to be much less dependent on the size of the basis set than the energies themselves. These two conditions allow to construct the true stabilization energy of extended complexes as a sum of extrapolated complete basis set limit of MP2 stabilization energy and [MP2–CCSD(T)] term determined in a smaller basis set. The ab initio pair intermolecular potential results have been fitted to suitably chosen analytical formulas, and tested on experimental data for the second virial coefficients, spectral characteristics, and scattering data. For argon, an excellent agreement between the theoretical and the experimental values has been found. In the case of krypton and xenon the agreement is not as good but still acceptable.

Adjustment of Perdew-Wang exchange functional for describing van der Waals and DNA base-stacking interactions

In order to accurately describe the van der Waals interaction between rare-gas atoms by the density functional theory, we adjusted the exchange-functional developed by Perdew and Wang (PW). The van der Waals interactions of He, Ne, Ar and Kr dimers were investigated. The results clarified that the adjustment improves the overestimation of the interactions by the original PW exchange-functional, providing the qualitatively accurate trend in van der Waals interactions of He, Ne, Ar and Kr dimers. However, we also found that the adjusted functional for He and Ne underestimates the DNA base-stacking interaction between cytosine monomers. This may indicate that the PW exchange-functional requires a further modification or a van der Waals correction in order to give accurate DNA base-stacking interaction.

Ab initio and DFT studies for accurate description of van der Waals interaction between rare‐gas atoms

AbstractTo evaluate the accuracy of density functional theory (DFT) for describing van der Waals interaction between rare‐gas atoms, we performed coupled‐cluster theory restricted to single, double, and noniterative triple excitations [CCSD(T)], fourth‐order perturbation theory including single, double, and quadruple substitutions [MP4(SDQ)], and several DFT calculations for He, Ne, Ar, and Kr dimers. The results clarified that (1) CCSD(T) and MP4(SDQ) with an “adjusted” diffuse basis‐set reproduce the experimental trend in binding energies as well as equilibrium distances of these dimers, (2) MP3 and MP2 underestimate the binding energies, (3) Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar (B3LYP) and B3PW91 completely fail to describe the binding, and (4) Perdew–Wang exchange‐correlation functional (PW91PW91) and its modified ones (MPWPW91 and MPW1PW91) can provide the binding states, although the calculated binding energies cannot reproduce the experimental trend in binding energies. Therefore, we conclude that the above DFT functionals cannot quantitatively describe the van der Waals interaction between rare‐gas atoms and that the Perdew‐Wang–type exchange functional needs further improvement to describe the interaction. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

Control of transcription by Krüppel through interactions with TFIIB and TFIIE beta.

The zinc-finger protein Krüppel (Kr) is an integral part of the Drosophila segmentation gene cascade and is essential in organogenesis during later embryonic development. In tissue culture, Kr regulates transcription. Monomeric Kr can act as a transcriptional activator, whereas Kr dimers formed at high concentrations cause repression. Here we show that Kr-dependent control of transcription involves functional interactions with components of the basal RNA polymerase II transcription machinery, which includes the initiation factors TFIIA, B, E, F, H and I (refs 10, 11) as well as the TATA-binding protein (TBP) and TBP-associated factors (TAFs) contained in the multisubunit TFIID (ref. 12). Our results indicate that when acting from a site close to a basal promoter, monomeric Kr interacts with TFIIB to activate transcription, whereas an interaction of the Kr dimer with TFIIE beta, a subunit of TFIIE, results in transcriptional repression.

Dissociation energy of neutral and ionic benzene-noble gas dimers by pulsed field threshold ionization spectroscopy

Delayed pulsed field threshold ionization of clusters excited to high long-lived Rydberg states is used to study their dissociation behavior. Benzene–Ar and benzene–Kr dimers are excited by resonance enhanced two-photon ionization to Rydberg levels close to various ionization thresholds. The field ionized threshold ions are monitored and separated from the non-energy-selected ions in a reflecting field mass spectrometer with high mass resolution. The appearance of threshold ions at the daughter ion mass indicates the onset of a dissociation process. Daughter ions are first observed for the 16161(3/2) level of the two investigated dimers. This leads to an upper limit of the dissociation energy of benzene–Ar of 340 cm−1 which is probably higher than the true dissociation energy. For the first time threshold ions are observed for large internal energies of some 5 eV in the core indicating that high Rydberg states maintain their long lifetime even if the core is electronically or vibrationally excited by several eV.