Metastable Rare Gas Atoms Research Articles

Interaction of excited He and Ne rare gas metastable atoms with the CHF2Cl molecule

We studied the Penning ionization of the CHF2Cl molecule with He and Ne metastable atoms (He* and Ne*). We measured the electron kinetic energy and the time-of-flight mass spectra; we also determined the branching ratio for the parent ion and charged CHF+2, CHFCl+, HCF+/CF+ and Cl+ fragments. These data led us to discuss the dissociation channels for all the energetically-accessible electronic states of the ionized molecule. We evidenced a marked contrast in the fragment ion proportions for Ne*–CHF2Cl and He*–CHF2Cl systems, and related it to the difference in polarizability and internal energy of the He* and Ne* atoms.

Experimental and theoretical investigation of even mp51/2 np′ autoionizing resonances of rare gas atoms

Using experimental set-ups involving single photon excitation of metastable rare gas atoms Rg(mp5(m + 1)s, J = 2, 0) by a pulsed frequency-doubled dye laser in conjunction with time-of-flight ion detection, we have investigated several even Rg(mp51/2 np′) autoionizing resonances of the heavier rare gas atoms Rg = Ne − Xe (m = 2–5) at experimental bandwidths of 0.06 cm−1 (Ne) and about 0.25 cm−1 (Ar, Kr, Xe). New level energies (quantum defects) and widths for these resonances have been derived by a Fano-type lineshape analysis, thus yielding reduced resonance widths. The experimental spectra and the resonance parameters are compared with theoretical calculations which are based on the configuration interaction Pauli–Fock approach, including core polarization. For Rg = Ne, good agreement between the measured and the calculated results is observed. For the heavier rare gases, significant deviations between some of the existing experimental data and the theoretical results are found, indicating the need for further studies.

A high flux, liquid-helium cooled source of metastable rare gas atoms

We have developed a novel, high flux source of metastable rare gas atoms (helium, neon and argon) that uses liquid helium cooling to reduce the initial atomic velocity. Fluxes exceeding 1014 atoms/ster/s with He and Ne were obtained. With average velocities of ∼600 m/s for He and ∼300 m/s for Ne and Ar, this source will enable simpler, more compact beam lines for loading magneto-optical traps.

Low-pressure source of slow metastable rare gas atoms

We investigate the properties of a commercial inverted magnetron pressure gauge for use as a source of slow metastable rare gas atoms. We find that the velocity distribution of the atoms as well as the pressure dependence of the output flux agree with a simple model. This shows that the low-velocity output of the source is enhanced over the Maxwell–Boltzmann form due to a velocity-dependent excitation probability. For argon, the center-line intensity per unit area of the source is measured to be greater than 4.2×1015 Ar 1s5 atoms/(s sr m2) at a pressure of 23 mPa. When observing the entire source area, the center-line intensity is at least 2.6×1011 Ar 1s5 atoms/(s sr).

The interaction of excited He, Ar and Ne metastable atoms with the CF2Cl2 molecule**This paper is dedicated to Professor F M E Tuffin on the occasion of his retirement.

We studied Penning ionization of the CF2Cl2 molecule by neon and helium metastable atoms. In the case of the neon ionizing particle, we measured the electron kinetic energy as well as mass spectra; for helium metastable atoms, only the mass spectrum was recorded. We, therefore, obtained the branching ratios for the heavy charged particles produced in both interactions. In this report we will discuss the mechanism involved in the production of metastable halogen atoms in the dielectric barrier discharge further to the use of rare gases/CF2Cl2 mixtures. We show that this process needs a two-stage reaction. Ground state free halogen atoms are formed over the first stage by Penning ionization, charge transfer, dissociate excitation and ionization. Therefore, metastable halogen atoms can be produced by excitation transfer process in the second stage through interaction with metastable rare gas atoms.

An intense, slow and cold beam of metastable Ne(3s) 3 P 2 atoms

We employ laser cooling to intensify and cool an atomic beam of metastable Ne(3s) atoms. Using several collimators, a slower and a compressor we achieve a ^{20}Ne^* flux of 6 10^{10} atoms/s in an 0.7 mm diameter beam traveling at 100 m/s, and having longitudinal and transverse temperatures of 25mK and 300microK, respectively. This constitutes the highest flux in a concentrated beam achieved to date with metastable rare gas atoms. We characterize the action of the various cooling stages in terms of their influence on the flux, diameter and divergence of the atomic beam. The brightness and brilliance achieved are 2.1 10^{21} s^{-1} m^{-2} sr^{-1} and 5.0 10^{22} s^{-1} m^{-2} sr^{-1}, respectively, comparable to the highest values reported for alkali-metal beams. Bright beams of the ^{21}Ne and ^{22}Ne isotopes have also been created.

Metastable rare gas atoms scattered by nano- and micro-slit transmission gratings

The transmission of metastable argon atoms through nano-slit or micro-slit gratings is studied by use of time of flight and angular analysis. This transmission departs from the simple geometric one essentially by two ways: (i) the elastic or diagonal part of the van der Waals (vW) interaction with the solid causes an angular narrowing of the emerging beam; (ii) the off-diagonal vW interaction induces the exothermal fine structure transition 3 P 0↦3 P 2 (ΔE = 175 meV) leading to large scattering angles; the resulting angular distribution is very sensitive to the roughness of the surface in the direction of the depth. An extension of these experiments to transversally coherent beams is proposed. It should be considered as a first step towards a new type of interferometer in which the inelastic diffraction makes the gratings work as beam splitters or mirrors.

Long-range interaction of two metastable rare-gas atoms

We present semiempirical calculations of long-range van der Waals interactions for two interacting metastable rare-gas atoms Ne through Xe. Dispersion coefficients $C_6$ are obtained for homonuclear molecular potentials asymptotically connecting to the $ns(3/2)_{2} + ns(3/2)_{2}$ atomic states. The estimated uncertainty of the calculated $C_6$ dispersion coefficients is 4%.

A highly sensitive electron spectrometer for crossed-beam collisional ionization: A retarding-type magnetic bottle analyzer and its application to collision-energy resolved Penning ionization electron spectroscopy

A highly sensitive electron energy analyzer which utilizes a “magnetic bottle” combined with a retarding electrostatic field has been developed for Penning ionization electron spectroscopy. A beam of metastable rare-gas atoms is crossed with a continuous supersonic sample beam in the source region of the analyzer. The emitted electrons are collected by an inhomogeneous magnetic field (the magnetic bottle effect) with a high efficiency of nearly 4π solid angle, which is more than 103 times higher than that of a conventional hemispherical analyzer. The kinetic energy of electrons is analyzed by scanning the retarding field in a flight tube of the analyzer in the presence of a weak magnetic field. The velocity of the metastable atoms can also be resolved by a time-of-flight method in the present instrument. Examples of Penning ionization electron energy spectra as a function of collision energy are presented for Ar and N2 with metastable He*(2 3S) atoms. This instrument has opened the possibility for extensive studies of Penning ionization electron spectroscopy for low-density species, such as clusters, ions, electronically excited species, unstable or transient species, and large molecules with low volatility.

Dynamics of the Penning Ionization of Fullerene Molecules by Metastable Neon Atoms

The collision energy dependence of the cross section for the Penning ionization of C60 molecules by metastable neon atoms has been measured in the 0.035−0.5 eV range in a crossed beam experiment. The results show a decreasing trend (∼20%) in the low-energy range up to 0.06 eV, with a slightly increasing dependence in the higher energy range. This behavior is interpreted in terms of the characteristics of the intermolecular interaction: an electron transfer can be possible from the metastable rare gas atom to the C60 molecule with the formation of an ion-pair collision complex. At low collision energy the system evolves mainly adiabatically and the ionization occurs mainly from the ion-pair complex. However, at higher collision energies, nonadiabatic transitions become possible and the systems can remain partially “trapped” within the higher adiabatic state with a consequent increase of the ionization probability.

Calculated cross sections for the electron-impact ionization of metastable atoms

The semiclassical Deutsch-Märk (DM) formalism was used to calculate absolute cross sections for the electron-impact ionization of metastable atoms such as metastable rare-gas atoms and metastable mercury and cadmium atoms from threshold to 200 eV. Systematic trends in the calculated cross section data are discussed and a comparison is made with available experimental data and with other calculations. Specifically, we calculated separately the contributions to the ionization cross sections arising from the removal of the single excited electron in the outermost subshell and the removal of the lower-lying inner-shell electrons.

The influence of core polarization on photo-ionization of alkali and metastable rare gas atoms near threshold

The effect of the polarization of the atomic core by the outer electron on near-threshold photo-ionization of alkali atoms (Na-Cs) and metastable rare gas atoms (Ne*-Xe*) is investigated. The variational principle is applied to compute the core polarization potential and thereby obtain dipole polarizabilities of the alkali and rare gas ions. The calculated potential is considerably deeper inside the atomic core than the previously used core polarization potentials. Inclusion of the core polarization potential leads to a better agreement of calculated near-threshold photo-ionization cross sections with experimental data in the threshold region, especially for the alkali atoms.

Diatomic potential well depths from analyses of high-resolution electron energy spectra for autoionizing collision complexes

High-resolution energy spectra of electrons released in Penning ionization collisions of metastable rare gas atoms Rg*(ns) (Rg = He, Ne, Ar, Kr, Xe) with several open-shell and closed-shell atoms are analyzed to determine the well depth of the potential energy curve which describes the respective autoionizing collision complex. We thereby elucidate trends in the chemical interaction of Rg* with closed-shell target atoms A(ns2) and establish a basis for detailed comparison with the respective interactions involving open-shell, ground state alkali atoms A(ns). From electron energy spectra due to␣associative ionization (RgH+ formation) in Rg* + H(1s) collisions, we determine binding energies for the RgH+(1Σ) ground state potential (Rg = Ne, Ar, Kr, Xe) with uncertainties around 0.03 eV.

Penning ionization of C 60 molecules

A mass-spectrometric study of Penning ionization of C 60 with metastable rare-gas atoms (Rg=He, Ne, Ar, Kr and Xe) shows that the sole channel is C 60 + formation. The ionization cross-sections, at an average collision energy of 0.05 eV, strongly decrease from helium to xenon. The interaction potentials for C 60–Rg *, C 60 +–Rg, C 60–Rg and C 60 −–Rg +, and matrix elements for the coupling of the C 60–Rg * and C 60 −–Rg + interactions at the crossing point, have been estimated using recently proposed correlation formulas. The trend of the ionization cross-sections can be explained by the low-energy collisions between Rg * and C 60, characterized by the formation of an ion-pair C 60 −–Rg + intermediate with a decreasing probability on going from lighter to heavier rare gases.

Booster for ultra-fast loading of atom traps

We propose a 2D magneto-optical compressor with a very large 40 mm diameter acceptance area to funnel the low velocity tail of the Maxwell–Boltzmann distribution (v≤100 m/s) in a low pressure discharge (Ne*) or alkali vapor cell (Na) into a well-collimated (10 mrad) bright beam of 107 to 108 atoms/s for Ne* or 2×1011 atoms/s for Na, leaving the cell through a 1 mm orifice. After axial cooling in an isotropic light field, resulting in an axial velocity distribution with 〈v〉=8 m/s with a FWHM Δv=3 m/s, this beam can be efficiently loaded into an atom trap. For rubidium, the predicted flux is 8×1011 atoms/s. Compared to all other alkali vapor-cell schemes, the gain in loading rate is a factor of 20 to 100, a major boost for achieving Bose–Einstein condensation. For the metastable rare gas atoms, it is the first table-top scheme for experiments with atom traps.

Ionizing Collisional Rate of Metastable Rare-Gas Atoms in an Optical Lattice

Ionizing collisional rate of metastable krypton and argon atoms in an optical lattice k{sub la tt ic e} is compared with that in free space k{sub free} . Reduction of the collisional rate is observed for krypton atoms. However, the magnitude of reduction is no more than a factor of 2 at the laser detuning of 7GHz. The ratio k{sub la tt ic e}/k{sub free} is found to change proportional to the square root of the excitation rate of atoms from the 1s{sub 5} metastable state to the 2p{sub 9} state by the lattice laser. The mechanism that prevents a larger reduction is discussed. {copyright} {ital 1997} {ital The American Physical Society}

A nozzle beam source for the production of metastable rare gas atoms

An atomic beam source for the production of metastable rare gas atoms is presented. The set-up is based on a supersonic gas expansion combined with a negative point-to-plane discharge. In contrast to similar devices, there are no perturbing electromagnetic fields in the low-pressure region. The properties of the discharge and the flux of metastables as functions of the discharge parameters have been investigated. Results for helium and argon are shown.

A 2-dimensional detector with high spatial and temporal resolution for metastable rare gas atoms

We describe a detector for metastable rare gas atoms which allows the investigation of transverse atomic beam distributions on the single atom level with lateral dimensions of 1 \(\mu\)m, which occur frequently in the field of atom optics. In contrast to existing detection techniques, the conversion step from the metastable atom to an electron is separated from the charge amplification to improve spatial resolution. The conversion is performed at a metal surface, which is followed by an electron-optical system imaging the electron distribution with a proper magnification onto a single electron detection unit. The spatial resolution that we achieve with this technique is on the order of 1 \(\mu\)m, the temporal resolution on the order of 1 \(\mu\)s. The application of the detector for atom interferometry is discussed.

Production of Ultrabright Slow Atomic Beams Using Laser Cooling

We propose to use a three-step transverse and longitudinal cooling scheme, to compress and collimate a strongly diverging flow of metastable rare gas atoms. Simulations show that an atom beam flux of 1010 8−1 in a small diameter (−1 ) atomic beam could be achieved. This technique can be extremely valuable in many areas of atomic physics, e.g. in (electron) spectroscopy and atomic collision physics where high beam densities are desirable.

Studies on State‐to‐State Energy Transfer of Electronically Excited Atoms and Molecules

AbstractRotationally inelastic collisions of NH2( Ã2A1), ∑(0,9,0), 303, 101 have been studied by measuring the dispersed fluorescence spectra at molecular beam conditions. The results show that the angular momentum transfer rule is much more successful than is that predicted by energy gap law for fitting the rotational energy transfer rate. For ΔN < 2 the transfer rates are getting slow down. Downward transfer rates are faster than those of upward transfer. With same angular momentum transferred, the transfer rates for Δka = 0 process are larger than those for Δka≠0. It is also found that rotation transfer process is a very efficient way for decaying of the initially pumped levels. About 60% of the initially pumped 303 is colliding into other rotational levels. Energy transfer reactions of metastable rare gas atoms (Rg*) with N2, NH3, CS2 were investigated by measuring the emission spectra. The preferential population of n(A″) of NH(c1II) was found in He(23S) + NH3 reaction, the experimental data shows II(A″)/II(A′) = 1.2 at J′ < 13. A high vibrational excitation and low rotational excitation of N2(C3n) were observed in Ne(3P02) + N2 reaction comparing with Ar(3P0.2) + N2 reaction. The detailed vibrational populations of CS2+ (Ã, B̃) achieved by He(23S)/Ne(3P0.2) + CS2 reaction are different from those obtained by PES. The vibrational distributions of CH(A2Δ) obtained by He(23S) + CHC13 (CH3NO2) reactions were discussed based on statistical theory, special attention was paid to reveal the role played by tie angular momentum restriction in this process. The result on energy transfer between N2(a1 Π) and CO(X1 ∑) was firstly presented by VUV emission spectra at single collision condition. The mechanisms of energy transfer related to some of the reactions mentioned above were also discussed in the text.