Argon Dimer Research Articles

A Unified Perspective on the Nature of Bonding in Pairwise Interatomic Interactions

Different classes of ground electronic state pairwise interatomic interactions are referenced to a single canonical potential using explicit transformations. These approaches have been applied to diatomic molecules N2, CO, H2(+), H2, HF, LiH, Mg2, Ca2, O2, the argon dimer, and one-dimensional cuts through multidimensional potentials of OC-HBr, OC-HF, OC-HCCH, OC-HCN, OC-HCl, OC-HI, OC-BrCl, and OC-Cl2 using accurate semiempirically determined interatomic Rydberg-Klein-Rees (RKR) and morphed intermolecular potentials. Different bonding categories are represented in these systems, which vary from van der Waals, halogen bonding, and hydrogen bonding to strongly bound covalent molecules with binding energies covering 3 orders of magnitude from 84.5 to 89,600.6 cm(-1) in ground state dissociation energies. Such approaches were then utilized to give a unified perspective on the nature of bonding in the whole range of diatomic and intermolecular interactions investigated.

Core photoionization of the argon dimer in the photon-energy range of 255–340 eV studied by a photoelectron-photoion-photoion coincidence technique

Single-photon multiple ionization of the argon dimer van der Waals complex, ${\mathrm{Ar}}_{2}$, is studied by the photoelectron-photoion-photoion coincidence technique using synchrotron radiation in the photon-energy range of 255--340 eV, which covers the Ar 2$p$ and Ar 2$s$ ionization continua. Dissociation processes into ${\mathrm{Ar}}^{+}+{\mathrm{Ar}}^{+}$, ${\mathrm{Ar}}^{+}+{\mathrm{Ar}}^{2+}$, ${\mathrm{Ar}}^{+}+{\mathrm{Ar}}^{3+}$, and ${\mathrm{Ar}}^{2+}+{\mathrm{Ar}}^{2+}$ ion pair channels are observed. The ${\mathrm{Ar}}^{+}+{\mathrm{Ar}}^{+}$ and ${\mathrm{Ar}}^{+}+{\mathrm{Ar}}^{2+}$ channels show the most intense ion-ion coincidences, compared to other observed dissociative channels. For the four observed channels the intensities are integrated and compared as functions of photon energy.

Ion impact induced ionization/fragmentation dynamics of rare gas Dimers

We have measured the ionization and fragmentation of Helium, Neon and Argon Dimers induced by ion impact and observed two different pathways, the sequential ionization on each atom and the interatomic Cou-lombic decay.

Observation of interatomic Coulombic decay and electron-transfer-mediated decay in high-energy electron-impact ionization of Ar2

We measured the kinetic energy distributions of the fragment ions of doubly and quadruply ionized argon dimers using 3000 eV electron impact. For the dissociation of (Ar${}_{2}$)${}^{2+}$, the peak that indicates radiative charge transfer is observed, where the outer-shell ionization (dominant in highly charged ion collision) and the inner-shell ionization (preferential in x-ray experiments) have approximately equal contributions. For the dissociation of (Ar${}_{2}$)${}^{4+}$, the interatomic Coulombic decay and electron-transfer-mediated decay are first observed in the electron-impact process.

Ion-impact-induced interatomic Coulombic decay in neon and argon dimers

We investigate the contribution of interatomic Coulombic decay induced by ion impact in neon and argon dimers (Ne${}_{2}$ and Ar${}_{2}$) to the production of low-energy electrons. Our experiments cover a broad range of perturbation strengths and reaction channels. We use 11.37 MeV/u S${}^{14+}$, 0.125 MeV/u He${}^{1+}$, 0.1625 MeV/u He${}^{1+}$, and 0.150 MeV/u He${}^{2+}$ as projectiles and study ionization, single and double electron transfer to the projectile, as well as projectile electron loss processes. The application of a COLTRIMS reaction microscope enables us to retrieve the three-dimensional momentum vectors of the ion pairs of the fragmenting dimer into Ne${}^{q+}$-Ne${}^{1+}$ and Ar${}^{q+}$-Ar${}^{1+}$ ($q=$ 1, 2, 3) in coincidence with at least one emitted electron.

Efficient site-specific low-energy electron production via interatomic Coulombic decay following resonant Auger decay in argon dimers

We identified interatomic Coulombic decay (ICD) channels in argon dimers after spectator-type resonant Auger decay $2p^{-1}~3d \to 3p^{-2}3d, 4d$ in one of the atoms, using momentum resolved electron-ion-ion coincidence. The results illustrate that the resonant core excitation is a very efficient way of producing slow electrons at a specific site, which may cause localized radiation damage. We find also that ICD rate for $3p^{-2}4d$ is significantly lower than that for $3p^{-2}3d$.

Steering the Nuclear Motion in Singly Ionized Argon Dimers with Mutually Detuned Laser Pulses

We demonstrate that the vibrational nuclear motion of singly ionized argon dimers can be controlled with two ultrashort laser pulses of different wavelengths. In particular, we observe a striking "gap" in the pump-probe-delay-dependent kinetic-energy release spectrum only if the probe-pulse wavelength exceeds the pump-pulse wavelength. This "frustrated dissociation effect" is reproduced by our two-state quantum mechanical model, validating its interpretation as a pump-pulse-initiated population transfer between dipole-coupled Born-Oppenheimer electronic states of the dissociating Ar(2)(+) molecular ion. Our numerical results also reproduce the measured collapse and fractional revival of the oscillating Ar(2)(+) nuclear wave packet, and, for single-pulse dissociation, the decrease of the kinetic-energy release with increasing laser wavelength.

Theoretical Investigation of the Dispersion Interaction in Argon Dimer and Trimer

The present work attempts to assess and evaluate the performance of some new DFT methods in describing van der Waals (vdW) complexes that are characterized by the dominance of pure dispersion interactions. To achieve this goal, Argon dimers (Ar2) and trimers (Ar3) were investigated. As a reference calculation, the correlation interaction energy have been computed at the CCSD(T) level using the aug-correlated family of basis sets pVXZ (where X=2,3,4). Extrapolation to the CBS limit has been carried out and the behavior of the potential energy function has been analyzed and discussed. Correlation interaction energy has been computed at the MP2 and MP4 levels and compared to those calculated at the CCSD(T) method. Five new correlated DFT functionals, namely M06 and its long rang extension M06L, the B97-2 and its modified version B97-D which was deviseded for the dispersion interaction, and the PBEPBE and its correlated extension PBE0 methods have been used to compute the interaction energy in Ar2 and Ar3. The present work results indicate clearly that M06 and M06L did not only overestimate the equilibrium distance and depth but they also showed fluctuations in the potential energy curve near the minimum and along the dissociative arm. The B97-D and the PBE0 methods are much more reliable. However, these two later methods showed convergence problems when used to treat Ar3+; in addition to being extremely fast when compared to the CCSD(T) method extremely fast as compared to the CCSD(T). These features make them good candidate for investigating large vdW clusters. The BSSE has been estimated, analyzed and discussed. The relative stabilities of the excited states of Ar2 and Ar3 clusters together with those of the ionic species (Ar2+ and Ar3+)have been computed and analyzed.

Theoretical investigation of the dispersion interaction in argon dimer and trimer

The ultimate aim of the present work is to establish an acceptable level of computation for the van der waals (vdw) complexes that is able to pick up appreciable amount of dispersion interaction energy, reproduce the equilibrium separation within the acceptable limits and at the same time cost and time effective. In order to reach this aim vdw clusters where pure isotropic dispersion interaction occur, namely, Ar dimer and trime were investigated. Computations using different basis sets and at different levels of theory have been carried out. Three basis sets, namely, the 6-31++G**, the 6-311++G** and the aug-cc-pvdz basis set, were found superior to all other basis sets used. The high performance and relative small CPU time of the 6-31++G** basis set make it a good candidate for use with large vdw clusters, especially those of interest in biology. Three compound methods were applied in the present work, namely G1, G2 and G2 Moller-Plesset (MP2) and the complete basis set method, CBS-Q. These methods failed to detect the attraction dispersion interaction in the dimer. The predicted repulsive interaction seems dominant in all these methods. Some of the recently developed Density Functional Theory (DFT) methods that were parameterized to account for the dispersion interaction were also evaluated in the present work. Results come to the conclusion that, in contrast to the claims made, state-of-the-art Density Functional Theory methods are incapable of accounting for dispersion effects in a quantitative way, although these methods predict correctly the inter-atomic separations and are thus considered a real improvement over the conventional methods. BS-SE has been computed, analyzed and discussed.

Asymmetry of charge sharing in argon dimer observed in the reaction plane

Low-energy collisions of Ar9+ with Ar2 were conducted and charge sharing in the asymmetric dissociation channels was analyzed. The correlation of scattering direction of projectile and orientation of the target dimer indicates that the atom closer to the projectile is preferentially ionized.

Theoretical Investigation of Selenium Interferences in Inductively Coupled Plasma Mass Spectrometry

Structures, heats of formation, ionization energies, and proton affinities of selenium, argon dimer, argon-chlorine, and their hydrides (Se, SeH, SeH2, ArH, ArH2, Ar2, Ar2H, Ar2H2, ArCl, and ArHCl) are estimated by quantum chemistry calculations using G3, G4, and W1 composite methods and coupled cluster approach at the CCSD(T)/aug-cc-pVTZ levels. Thermochemistry of the reactions between ions A(+) = Se(•+), SeH(+), SeH2(•+), SeH3(+), Ar2(•+), Ar2H(+), Ar2H2(•+), Ar2H3(+), ArCl(+), ArClH(•+), and ArClH2(+) with various neutral gas G commonly used in dynamic reaction chamber-inductively coupled plasma-mass spectrometry (DRC-ICP-MS) (G = H2, CH4, NH3, O2, CO, CO2, NO, and N2O) has been investigated.

A compact vacuum UV excilamp on argon dimers

The energy and spectral characteristics of the argon dimer emission with the maximum at a wave-length of ∼126 nm under excitation by a pulse-periodic discharge in a gas flow with pressures higher than the atmospheric pressure are studied. A compact excilamp has been designed for obtaining radiation in the vacuum ultraviolet spectrum region. The minimal argon flow velocities are determined, at which cooling is effected by convective gas ejection from the discharge region. This allows one to form a diffusion discharge with a stable radiation power density. It is shown that, when the flow velocity is 0.5 m3/h, the radiation power density of an Ar2* molecule is >100 μW/cm2 behind a LiF window with ∼10% transmission at a wavelength of 126 nm. It is shown that the use of a windowless design and an increase in the gas flow velocity allows an increase in the radiation power density up to 10 mW/cm2.

Wannier functions approach to van der Waals interactions in ABINIT

The method to calculate van der Waals interactions based on maximally localized Wannier functions (MLWFs), proposed by Silvestrelli [Phys. Rev. Lett. 100 (2008) 053002], has been implemented within the ab initio DFT program ABINIT. In addition to a brief review of the theoretical background behind this methodology, we present the details of the implementation, which will help users to assess van der Waals corrections in both molecular and periodic systems with a negligible additional computational cost. Some tests on argon dimer, argon FCC solid, benzene dimer and bilayer of graphene are presented. A discussion about the reliability of the method is also included.

Multiple Recapture of Electrons in Multiple Ionization of the Argon Dimer by a Strong Laser Field

We observe multiply frustrated tunneling ionization-induced dissociation of the argon dimers by intense linearly polarized ultrashort laser pulses. By measuring the kinetic energy release and angular distribution of the Coulomb explosion of up to eightfold ionized argon dimers, we can trace the recapture of up to two electrons to Rydberg states of the highly charged compound at the end of the laser pulse. Upon dissociation of the dimer, the Rydberg electron prefers to localize at the atomic ion with the higher charge state. We probe the electron recapture dynamics by a time-delayed weak pulse.

Nonadiabatic alignment of van der Waals--force-bound argon dimers by femtosecond laser pulses

We demonstrated that the weak van der Waals–force-bound argon dimer can be nonadiabatically aligned by nonresonant femtosecond laser pulses, showing periodic alignment and anti-alignment revivals after the extinction of the laser pulse. Based on the measured nonadiabatic alignment trace, the rotational constant of the argon dimer ground state is determined to be B0 = 0.05756 ± 0.00004 cm −1 . Noticeable alignment dependence of frustrated tunneling ionization and bond-softening induced dissociation of the argon dimer are observed.

Multiple-ionization and dissociation dynamics of a rare gas dimer induced by highly charged ion impact

Low-energy collision experiments of an argon dimer with Ar9+ were performed to measure branching ratios and kinetic energy release (KER) distributions for multiply ionized dimers. Two well-separated KER peaks are observed at 3.8 and 5.3 eV for the doubly ionized dimers, and are assigned to direct Coulombic dissociation and radiative electron capture followed by ionic dissociation, respectively. For the dissociation channels Ar2++Ar+, Ar3++Ar+ and Ar2++Ar2+, the KER distributions show a single peak, the positions of which agree well with those expected for Coulombic dissociation. The branching ratio of asymmetric charge sharing, Ar3++Ar+, is larger than that of symmetric charge sharing, Ar2++Ar2+. These results represent unambiguous evidence of a strong limitation of charge mobility across the Ar dimer.

Imaging of the Structure of the Argon and Neon Dimer, Trimer, and Tetramer

We Coulomb explode argon and neon dimers, trimers, and tetramers by multiple ionization in an ultrashort 800 nm laser pulse. By measuring all momentum vectors of the singly charged ions in coincidence, we determine the ground state nuclear wave function of the dimer, trimer, and tetramer. Furthermore we retrieve the bond angles of the trimer in position space by applying a classical numerical simulation. For the argon and neon trimer, we find a structure close to the equilateral triangle. The width of the distribution around the equilateral triangle is considerably wider for neon than for argon.

Electron-Transfer-Mediated Decay and Interatomic Coulombic Decay from the Triply Ionized States in Argon Dimers

We report the first observation of electron-transfer-mediated decay (ETMD) and interatomic Coulombic decay (ICD) from the triply charged states with an inner-valence vacancy, using the Ar dimer as an example. These ETMD and ICD processes, which lead to fragmentation of Ar(3+)-Ar into Ar(2+)-Ar(2+) and Ar(3+)-Ar+, respectively, are unambiguously identified by electron-ion-ion coincidence spectroscopy in which the kinetic energy of the ETMD or ICD electron and the kinetic energy release between the two fragment ions are measured in coincidence.

Asymmetry in Multiple-Electron Capture Revealed by Radiative Charge Transfer in Ar Dimers

We measured kinetic energies of the fragment ions of argon dimers multiply ionized by low-energy Ar(9+) collisions. For (Ar2)(4+) dissociation, the asymmetric channel (Ar(3+) + Ar(+)) yield is found unexpectedly higher than the symmetric channel (Ar(2+) + Ar(2+)) yield in contrast with previous observation for covalent molecules or clusters. For the dissociation channel (Ar2)(2+)→Ar(+) + Ar(+), two well-separated peaks were observed, clearly evidencing that the direct Coulombic dissociation and the radiative charge transfer followed by ionic dissociation alternatively occur for the dicationic dimers. The respective intensity of these two peaks provides a direct mean to unravel the respective proportion of one-site and two-site double-electron capture, which are found equal for this collision system.

Dispersion Interactions between Rare Gas Atoms: Testing the London Equation Using ab Initio Methods

A computational chemistry experiment is described in which students can use advanced ab initio quantum mechanical methods to test the ability of the London equation to account quantitatively for the attractive (dispersion) interactions between rare gas atoms. Using readily available electronic structure applications, students can calculate the interaction energies of the four rare gas dimers (He2, Ne2, Ar2, and Kr2) and the six heterodimers at internuclear distances large enough to warrant neglecting repulsive interactions. The London C6 coefficients, obtained from experimental polarizability volumes and ionization energies, are used with the calculated interaction energies to test the London equation. The role of the higher-order C8 term in accounting for dispersion interactions in the dimers is examined. In addition, students calculate a portion of the argon dimer interaction potential at large internuclear separations and compare this potential with that predicted by the London equation.