Potential‐Energy Curves for the He2 Molecule
01 May 1970-Journal of Chemical Physics (American Institute of PhysicsAIP)-Vol. 52, Iss: 9, pp 4469-4474
TL;DR: In this paper, potential energy curves for diatomic He molecules constructed by Rydberg-Klein-Rees procedures were constructed for the first time using RKR procedures.
Abstract: Potential energy curves for diatomic He molecules constructed by Rydberg-Klein-Rees procedures
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TL;DR: In this paper, the neutral beam time-of-flight distribution has three peaks associated with distinct groups of large and small clusters, and atoms, and the dependence of the various charged and neutral metastable fragment currents on the bombarding electron energy reveals that each has a unique appearance potential.
Abstract: Clusters are produced by expanding high pressure (P0≤20 bar), low temperature (T0≥5 K) helium gas through a 5 μm nozzle into a vacuum. The neutral beam time‐of‐flight distribution has three peaks which we associate with distinct groups of large and small clusters, and atoms. The beam is ionized by electron impact and the resulting time resolved charged fragment mass distribution reveals in addition to previously observed anomalies (‘‘magic numbers’’) a new strong He+4 signal at high source pressures and low temperatures. The dependence of the various charged and neutral metastable fragment currents on the bombarding electron energy reveals that each has a unique appearance potential. A comparison with the calculated energy required for an electron to create various electronic excitations in the interior of a large cluster indicates that the production and dynamical evolution of metastable 3S1 atomic and a 3Σ+u molecular excitations plays a significant role in the formation of charged fragments from large ...
138 citations
TL;DR: In this paper, a molecular beam time-of-flight method is used to measure the translational energy of high-Rydberg molecular orbital and the fragment kinetic energy distributions are discussed in terms of known and predicted states of O2 and O2+.
Abstract: Excitation of O2 by low energy electrons leads to its dissociation with the formation of metastable oxygen atoms. The metastable atoms which have been detected are in the 3s5S0 state at 9.14 eV and in long‐lived high‐Rydberg states. A molecular beam time‐of‐flight method is used to measure their translational energy. Electron impact excitation functions are given for the formation of metastable atoms. High‐Rydberg atoms result from dissociation of initially formed high‐Rydberg molecules. Because a high‐Rydberg molecular orbital is nonbonding, dissociation is determined by states of the core O2+ ion. This mechanism is supported by general agreement between the observed kinetic energy distribution of high‐Rydberg atoms and the kinetic energy distribution of O+ from dissociative ionization of O2. The fragment kinetic energy distributions are discussed in terms of known and predicted states of O2 and O2+.
92 citations
TL;DR: A review of the status and properties of coherent sources of ultraviolet radiation is presented in this article, which includes a wide range of developments concerning atomic and molecular systems useful for generating wavelengths below 4000 A, as well as progress in alternative methods of ultraviolet production.
Abstract: A review of the status and properties of coherent sources of ultraviolet radiation is presented. This includes a wide range of developments concerning atomic and molecular systems useful for generating wavelengths below 4000 A, as well as progress in alternative methods of ultraviolet production. Particular emphasis is placed on recent advances in molecular bound-free systems whose operation is enhanced at high densities. It is believed that some of these systems may be scalable to sufficiently high-energy outputs to be useful in controlled fusion applications. A brief prognosis and discussion of future developments tending to the X-ray region are given.
69 citations
TL;DR: In this article, the development of excimers and excimer lasers are reviewed and the methods of pumping, operational characteristics and applications of the lasers are discussed in terms of their structure, spectroscopy and formation kinetics.
Abstract: The development of excimers and excimer lasers are reviewed The excimers of the noble gases (Xe
2
*
, Kr
2
*
, Ar
2
*
) and of the noble gas halides (eg KrF, XeCl) which, respectively, radiate in the vacuum ultra-violet and ultra-violet regions of the spectrum are described in terms of their structure, spectroscopy and formation kinetics and the methods of pumping, operational characteristics and applications of the lasers are discussed
57 citations
TL;DR: Helium droplets doped with Xe and Kr atoms were photoionized by using VUV synchrotron radiation from the Advanced Light Source and the resulting photoelectron images were measured, revealing multiple photoionization mechanisms and pathways for the photoelectrons to escape the droplet.
Abstract: Helium droplets doped with Xe and Kr atoms were photoionized by using VUV synchrotron radiation from the Advanced Light Source and the resulting photoelectron images were measured. A wide range of He droplet sizes, photon energies, and dopant pick-up conditions was investigated. Significant ionization of dopants was observed at 21.6 eV, the absorption maximum of 2p 1 P1 electronic excited state of He droplets, indicating an indirect ionization mechanism via excitation transfer. The photoelectron images and spectra reveal multiple photoionization mechanisms and pathways for the photoelectrons to escape the droplet. Specifically, they show sets of sharp peaks assigned to two mechanisms for Penning ionization of the dopant by He* in which the photoelectrons leave the droplet with no detectable energy loss, a broad, intense feature representing electrons that undergo significant energy loss, and a small amount of ultraslow electrons that may result from electron trapping at the droplet surface. The droplet-size dependence of the broad, intense feature suggests the development of the conduction band edge in the largest droplets seen here (〈N〉 ≈ 250,000). I. Introduction This work presents a study of photoionization of He nanodroplets doped with Xe and Kr atoms and the resulting photoelectron dynamics. It is motivated by our desire to understand the mechanism of photoionization in doped He droplets, as well as the transport and escape of the photoelectrons produced by this process. By doing so, we hope to gain insight into the coupling between charged particles and the He droplet environment. The experiments are performed by using tunable vacuum ultraviolet (VUV) synchrotron radiation to ionize the droplets and photoelectron imaging to analyze the resulting photoelectrons.
56 citations
References
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TL;DR: In this paper, it was shown that the theoretically expected forms of the potential curves of excited rare-gas molecules make dissociative recombination improbable for normal He atoms but more probable for other rare gas diatomic ions.
Abstract: Recent experimental work on helium jets has indicated that excited atoms result usually from collisional-radiative electron capture by atom ions (${A}^{+}+2e\ensuremath{\rightarrow}{A}^{*}+e$; etc.) rather than by dissociative recombination by molecule ions (${{A}_{2}}^{+}+e\ensuremath{\rightarrow}{A}^{*}+A$), while for the heavier rare gases, the latter process is apparently relatively important. It is shown in the present paper that the theoretically expected forms of the potential curves of excited ${\mathrm{He}}_{2}$ and other rare-gas molecules make dissociative recombination improbable for ${\mathrm{He}}_{2}^{+}$ but more probable for the other rare-gas diatomic ions. Available spectroscopic data and theoretical considerations make it fairly sure that many of the familiar excited states of ${\mathrm{He}}_{2}$ have high maxima in their potential curves, but that no pure repulsion curves, except the one for two normal He atoms, exist below the energy of ${\mathrm{He}}^{+}$ + He. Besides the stable states with stable ${\mathrm{He}}_{2}^{+}$ core ($1{{\ensuremath{\sigma}}_{g}}^{2}1{\ensuremath{\sigma}}_{u}$, ${^{2}\ensuremath{\Sigma}_{u}}^{+}$) plus a Rydberg electron, there must be others with a core ($1{\ensuremath{\sigma}}_{g}1{{\ensuremath{\sigma}}_{u}}^{2}$, ${^{2}\ensuremath{\Sigma}_{g}}^{+}$) which per se is unstable but which on addition of an electron in a sufficiently strongly bound Rydberg orbital is stable; consideration of these states makes possible a reasonable explanation of the Hornbeck-Molnar effect in helium. Statements analogous to those about potential curves and electron recombination in helium are applicable also to a large extent for hydrogen.
116 citations
76 citations
TL;DR: In this article, a new vacuum-uv absorption phenomena in helium are reported, and the most important of these consist of bands between 600 and 611 A. They are attributed to the transition A 1Σu+←X 1 Σg+ of He2.
Abstract: New vacuum‐uv absorption phenomena in helium are reported. The most important of these consist of bands between 600 and 611 A. Individual bands exhibit diffuse rotational structure and together form a υ′ progression. They are attributed to the transition A 1Σu+←X 1Σg+ of He2. Several rotational constants Bυ for the upper state are noted. The dissociation energy and the term value of the upper state are estimated. A minimum height for the potential “hump” in the upper state is determined to be 0.059 eV. The close connection between the emission and absorption bands of He2 around 600 A is indicated and discussed. The location of the He‐continuum (emission) peak is worked out in relation to the A‐state term value and the ground‐state potential function. A number of absorption bands were also observed in the range from 510–600 A. They are attributed to other singlet systems relating to ns and nd orbitals (n > 2).
66 citations
TL;DR: In this article, a detailed discussion of the methods of determination of reliable molecular constants in the presence of l uncoupling is presented, and the results applied to the 3d complexes of He2.
Abstract: The electronic transitions 3dσf3Σu+, 3dπf3Πu, 3dδf3Δu→3pσc3Σg+ of He2 are described and term values presented for a number of vibrational levels for the 10 components of the singlet and triplet 3d complex. A detailed discussion of the methods of determination of reliable molecular constants in the presence of l uncoupling is presented, and the results applied to the 3d complexes of He2. The following molecular constants (cm−1), which have been corrected for l‐uncoupling effects, are reported: StateωexωeBeαere(A)f3Δu1706.8235.107.2300.2291.0791f3Πu1661.4844.797.1360.2331.0862f3Σu+1635.7744.417.0710.2461.0912F1Δu1706.5935.0657.2300.2251.0791F1Πu1670.5740.037.1560.2351.0847F1Σu+7.0980.2461.0891.
50 citations