Xe Complexes Research Articles

Characterization of an organometallic xenon complex using NMR and IR spectroscopy

Photolysis of Re(iPrCp)(CO)2(PF3) in liquid or supercritical Xe yields two new compounds [Re(iPrCp)(CO)2Xe and Re(iPrCp)(CO)(PF3)Xe]. Re(iPrCp)(CO)(PF3)Xe has been characterized by NMR and IR spectroscopies. The compound is an organometallic Xe complex that has been characterized by using NMR spectroscopy and is shown to be longer-lived than other organometallic Xe complexes by IR spectroscopy. 19F, 31P, and 129Xe chemical shifts have been determined. The 129Xe chemical shift of Re(iPrCp)(CO)(PF3)Xe, delta -6,179, is a Xe shift that is significantly shielded, on the order of 1,000 ppm, with respect to free Xe. The coupling constants between coordinated 129Xe and both the 19F and 31P nuclei present have been extracted, confirming the identity of the compound. Observed line widths give a lower limit to the lifetime of the coordinated Xe of 27 ms at 163 K.

Theoretical study of the external heavy atom effect on phosphorescence of free-base porphin molecule

The radiative lifetime of phosphorescence of free-base porphin (H 2P) molecule and its complexes with noble-gas atoms are calculated by time-dependent density functions theory (TD DFT) with quadratic response functions for account of spin–orbit coupling and electric dipole activity. The complexes with Ne, Ar, Kr, and Xe are used to simulate the external heavy atom (EHA) effect on phosphorescence of the H 2P molecule in the corresponding noble gas matrices. The B3LYP functional and small basis set (3–21G) are used throughout the study and comparison of all complexes but other basis sets are also utilized to support the chosen approach. A slow radiative rate constant of free-base porphin phosphorescence (about 10 −3 s −1) is obtained with all basis sets being in the order of magnitude agreement with experimental estimations. A strong enhancement of the H 2P phosphorescence rate (by 360 times) is calculated for Xe complex; while for Ne, Ar, and Kr complexes, the enhancement is equal to 1.1, 1.3, and 10.3 times, respectively. In these complexes, the noble gas atom is disposed at 3.6 Å above the center of the porphin ring. In spite of shortcomings of the chosen simple model, the TD DFT calculations explain the most important features of the EHA effect on phosphorescence of free-base porphin. Calculations of the hyperfine coupling tensors for all magnetic nuclei in the lowest triplet state of H 2P molecule and its complexes with noble-gas atoms indicate an appreciable penetration of the spin density to the EHA region. This can be connected with the enhancement of spin–orbit coupling in the H 2P molecule.

Significant interactions between uranium and noble-gas atoms: coordination of the UO2+ cation by Ne, Ar, Kr, and Xe atoms.

A noble gas and an ignoble cation: A laser-ablated uranium cation reacts with O2 to give UO2+, which is found to form [UO2(Ng)n]+ (Ng=Ne, Ar, Kr, Xe) complexes on condensation with excess noble gas. Experiments with mixtures of noble gases lead to five new absorptions for the mixed [UO2+(Ng)x(Ng′)y] complexes and show that the coordination number is five for Ng=Ar, Kr, and Xe (see picture).

A Comprehensive Computational Study on OCH+-Rg (Rg = He, Ne, Ar, Kr, Xe) Complexes

The equilibrium geometries, harmonic vibrational frenquencies, and the dissociation energies of the OCH+-Rg (Rg = He, Ne, Ar, Kr, and Xe) complexes were calculated at the DFT, MP2, MP4, CCSD, and CCSD(T) levels of theory. In the lighter OCH+-Rg (Rg = He, Ne, Ar) rare gas complexes, the DFT and MP4 methods tend to produce longer Rg-H+ distance than the CCSD(T) level value, and the CCSD-calculated Rg-H+ bond lengths are slightly shorter. DFT method is not reliable to study weak interaction in the OCH+-He and OCH+-Ne complexes. A qualitative result can be obtained for OCH+-Ar complex by using the DFT method; however, a higher-level method using a larger basis set is required for the quantitative predictions. For heavier atom (Kr, Xe)-containing complexes, only the CCSD method predicted longer Rg-H+ distance than that obtained at the CCSD(T) level. The DFT method can be applied to obtain the semiquantitative results. The relativistic effects are expected to have minor effect on the geometrical parameters, the H+-C stretching mode, and the dissociation energy. However, the dissociation energies are sensitive to the quality of the basis set. The nature of interaction between the OCH+ ion and Rg atoms was also analyzed in terms of the interaction energy components.

The rotational spectra of oxirane⋯xenon (129Xe, Xe131, Xe132 Xe134, Xe136 isotopomers): Bond energy and dynamics of Xe

The pulsed jet millimeter wave spectra of five isotopomers of the weakly bonded oxirane⋯Xe complex have been measured. Information on the equilibrium conformation, dynamics and dissociation energy have been deduced. The equilibrium distance of Xe with respect to the center-of-mass of the molecules is 3.82 Å, with Xe tilted 15° from the perpendicular to the center-of-mass of the ring toward the oxygen atom. The dissociation energy is estimated, from the centrifugal distortion constant DJ, to be ≈3.9 kJ/mol.

Heavy-element effect on the splitting of the [formula omitted] state of the LiRg (Rg=Ar, Kr and Xe) complexes

The spin–orbit splittings A SO ( R) of the A 2Π state of LiRg (Rg=Ar, Kr and Xe) complexes have been obtained from the configuration interaction calculations using relativistic effective core potentials and two-component spinors. The results confirm that the mixing between the p orbitals of the lithium atom and the valence np orbitals (and not the Rydberg orbitals) of the rare gas (Rg) atom produces a large A SO ( R) for the A 2Π states at short internuclear distances. The spectroscopic constants for the ground and A states of LiRg complexes are also reported.

The characterisation and reactivity of (η5-C5H5)M(CO)3(Xe) (M = Nb or Ta) in solution at room temperature

Employing fast time-resolved infrared (TRIR) spectroscopy we have characterised CpM(CO)3(Xe) (M = Nb or Ta) at room temperature in supercritical Xe solution; CpM(CO)3(Xe) were found to exhibit a similar reactivity with CO to the corresponding alkane complexes, CpM(CO)3(n-heptane) and we report a trend in reactivity of the early transition metal Xe complexes.

Dynamics of dissipation processes in the Ag–Xe complex

2ω–2ω bleaching measurements of the ground state absorption and 2ω–1ω fluorescence dip measurements were carried out on the s–p transitions of Ag atoms in Xe matrices by ps laser pulses with 2ω corresponding to about 320 nm and 1ω to 640 nm. The absorption spectrum is analyzed in terms of a dynamic Jahn–Teller (JT) effect with a depth of the bound −JT state of about 30 meV and a pseudorotation frequency of about 20 ps. The −JT state seems to be rather long lived with a depopulation time of 3(±1) ps and a small energy dissipation rate of about 1 phonon per ps. Fluorescence occurs after a significant static lattice deformation accompanied by an energy relaxation of 0.4 eV. This static deformation and the energy relaxation to the emitting states proceed on a similar time scale of 3 ps which is very fast if the involved energies and the dissipation rate of about 30 phonons per ps are considered. The different rates are related to the different coupling to the lattice in the pseudorotating and the statically deformed geometry. Transient absorption is only observed in the relaxed state with σ=1.6(±0.5)⋅10−16 cm−2.

Photodynamics of charge transfer and ion-pair states of Cl2:Xe complexes in liquid Ar

Sequential two photon studies of Xe:Cl2 complexes in liquid Ar are reported. The first photon prepares the excited state complex Xe:Cl2(3Πu), which radiatively relaxes with a lifetime of 10±1 μs (22±2 μs for the uncomplexed Cl2(3Πu)). A second photon accesses either the molecular ion pair state, Xe:Cl+Cl−, or the contact charge transfer transition, Xe+Cl−2. The latter dissociates to Xe+Cl−+Cl even though the product is formed at threshold. The former undergoes charge rearrangement and decays radiatively via Xe+Cl−2 (2Σu)→XeCl2(1Σg). Analysis of the excitation and emission spectra of the key intermediate in laser induced harpoon reactions, Xe+Cl−2, leads to the conclusions that the complex is linear in both ionic and neutral states, and allows a direct contrast between dissociation dynamics on ionic versus neutral surfaces.

Proton Tunneling In 5‐Chlorotropolone‐M1 (M = Kr, Xe, CH4) Van Der Waals Complexes

The S1‐S0 fluorescence excitation spectra of 5‐chlorotropolone‐M1 (M = Kr, Xe, CH4) van der Waals (vdW) complexes in the region near the electronic origin have been measured in a supersonic free jet to investigate the effect of the vdW interactions on proton tunneling. Tunneling splittings have been observed in the vdW vibrations as well as in the transitions of the Kr and Xe complexes. The tunneling splitting of the 5‐chlorotropolone‐(CH4)1 complex is significantly smaller than those of the Kr and Xe complexes. It has been suggested that the vdW vibrations couple with intramolecular motions, leading to a higher potential energy barrier to tunneling in the CH4 complex. The results of the 5‐ chlorotropolone complexes have been compared to those of the tropolone complexes.

Visible absorption and infrared emission of CN–Xe in an argon matrix

The visible absorption of the B 2Σ←X 2Σ transition and the ground state vibrational infrared emission of the CN–Xe complex are studied in an argon matrix.

Vibrational relaxation of HCl as a function of xenon density: The role of HCl–Xe complexes

A treatment of the effect of vibrational predissociation of van der Waals complexes on vibrational relaxation rates [Chem. Phys. 29, 253 (1978)] has been extended by including V–V energy transfer between complexed and uncomplexed species and the possibility of different V–T/R relaxation rates for complexed and uncomplexed species. These modifications allow us to reproduce experimentally observed relaxation data for HCl(v=1) over two orders of magnitude in xenon density. The dependence of the vibrational relaxation rate on density is discussed as are the implications of the observed behavior on isolated binary collision formulations of vibrational energy relaxation processes.

Organometallic carbonyl substitution kinetics in liquid xenon by fast time-resolved IR spectroscopy

The reaction of Cp*Rh(CO)Xe (Cp* = C[sub 5]Me[sub 5]) with CO was studied using time-resolved IR spectroscopy of liquid rare gas solutions. IR spectra for Cp*Rh(CO)Xe were obtained using pulsed UV laser photolysis of Cp*Rh(CO)[sub 2] in liquid Xe and a rapid-scan FTIR spectrometer with 0.09-s time resolution. Assignment to the Xe complex was confirmed from the similarity of the spectra and lifetime of the complex when a mixture of Xe in liquid Kr was used. The reaction of Cp*Rh(CO)Xe with added CO is very fast, and the rate constant was measured by fast time-resolved IR spectroscopy to be (5.7 [+-] 0.6) [times] 10[sup 5] to (1.9 [+-] 0.2) [times] 10[sup 6] M[sup [minus]1] s[sup [minus]1] over the temperature range 202-242 K. The kinetics are consistent with an associative substitution mechanism with activation parameters for the bimolecular rate constant of log(A) = 8.8 [+-] 0.3 ([delta]S* = [minus]20 [+-] 1 cal/(mol K)) and E[sub a] = 2.8 [+-] 0.3 kcal/mol ([delta]H* = 2.4 [+-] 0.3 kcal/mol). 32 refs., 4 figs., 1 tab.

Xenon-129 NMR study of the copper(1+)-xenon interaction in CuNaY zeolites: generalization to the demonstration of Xe-nd10 interactions

1 29 Xe NMR spectroscopy is used to investigate copper-exchanged sodium zeolites having different levels of exchange. The unusual low-frequency chemical shift for the CuNaY zeolites confirms that when these solids are treated in vacuum at 500 o C, the copper is in the form of Cu + . As in the case of Ag + , of similar electronic structure, this shift is attributed to d 10 -d 0 donation from Cu + to Xe during the very short lifetime of the Cu + -Xe complex

Vibrational properties of Xe—fullerene adducts. A molecular dynamics approach

A molecular dynamics study of Xe complexes with fullerenes (C 60 and C 70) is presented. Two models are used to describe the intermolecular interactions between guest atom and fullerenes, with comparable results. Exohedral complexes may be approximated as van der Waals adducts of Xe with aromatic molecules, with similar equilibrium distances, binding energies and intermolecular frequencies. Endo-complexes are found to be strained due to Xe dimensions and with intermolecular modes much higher in frequency than in the exo-case. The effect of the guest atom on the vibrational dynamics of fullerenes is also investigated.

A b i n i t i o second- and fourth-order Mo/ller–Plesset study on structure, stabilization energy, and stretching vibration of benzene⋅⋅⋅X (X=He,Ne,Ar,Kr,Xe) van der Waals molecules

The C6v structure of benzene⋅⋅⋅X (X=He, Ne, Ar, Kr, Xe) complexes was investigated with second-order Mo/ller–Plesset (MP2) theory; for the benzene⋅⋅⋅He the whole potential-energy surface (PES) was also studied. The stabilization energy of the benzene⋅⋅⋅He was also determined at the fourth-order Mo/ller–Plesset (MP4) level; the respective MP4 stabilization energy is almost identical with MP2 stabilization energy which is due to the compensation of MP3 and MP4 contributions. The ab initio MP2 intermolecular distances agree nicely for all the complexes studied with the experimental value. While the stabilization energy of benzene⋅⋅⋅He and benzene⋅⋅⋅Ne (67 cm−1; 99 cm−1) is considerably smaller than that of benzene⋅⋅⋅Ar (429 cm−1), the intersystem distance differs less (3.32 Å, 3.50 Å, 3.53 Å). The stabilization energies and intersystem distances for benzene⋅⋅⋅Kr and benzene⋅⋅⋅Xe are 485 and 601 cm−1 and 3.71 and 3.89 Å, respectively. The PES of benzene⋅⋅⋅He differs from that of benzene⋅⋅⋅Ar and can be characterized as more isotropic. The harmonic and anharmonic stretching frequencies were determined for all the complexes; anharmonicity plays a crucial role only for the benzene⋅⋅⋅He complex. Theoretical and experimental stretching frequencies for benzene⋅⋅⋅Ar and benzene⋅⋅⋅Kr agree very well.

A comparison between the vibrational relaxation rate of HCl in liquid versus supercritical xenon

The vibrational relaxation of HCl has been studied in both liquid Xe at 289 K and supercritical Xe at 291 K. The rate of relaxation of HCl( v = 1) in supercritical Xe is identical to the relaxation rate in the liquid-phase at a common density. These results are consistent with the predictions of an isolated binary collision model for this system. This prediction is valid even if, as expected, HCl—Xe complexes are present in both the liquid and supercritical fluid as long as the nature and concentration of the complexes depend only on density and temperature.

Van der Waals bond lengths and electronic spectral shifts of the benzeneKr and benzeneXe complexes

Rotationally resolved UV-spectra are presented for the 6 1 0 bands of benzeneKr and benzeneXe complexes yielding precise rotational constants and van der Waals bond lengths for the ground and excited vibronic state, and electronic band shifts. These value complement the previously published data for the other rare gases and the various quantities have now been determined for all the benzene—rare gas complexes. Measured values of the bond length were used to calculate the band shifts from recent theoretical predictions. They are compared with the experimental values of this work.

Electrical characteristics of amorphous GaAs xP 1− x films formed by ion beam sputter deposition

The electrical properties of amorphous GaAsP films formed by Ion Beam Sputter Deposition is investigated using Xe ion beam or complex beam consist of Xe and PH 3 ions. Furthermore, relation between the electron mobility and the composition in a-GaAs x P 1− x film is discussed.

Vibronic-level-specific heavy-atom effect on the fluorescence decay of the rare gas complexes of 9-methoxyanthracene

Laser-induced fluorescence (LIF) spectroscopy is applied to study the dynamics of electronically excited van der Waals (vdW) complexes of 9-methoxyanthracene (MEOA) with Ar, Kr and Xe. The fluorescence decay features of these rare gas complexes vary widely depending on the number of coordinated atoms as well as on the vibronic levels of MEOA. The heavy-atom effect observed for the Kr and Xe complexes in the electronic origin is manifested more strongly in the vibronically excited 12 0 1 and 12 0 2 levels. Excitation to levels higher than 12 0 1 leads to vibrational predissociation of the complexes, yielding in many cases non-exponential decays with long-lived components (21–25 ns) which reflect the production of fragments in vibrationless states.