Benjamin Bederson

Atomic and Molecular Polarizabilities-A Review of Recent Advances

Publisher Summary This chapter focuses on the recent developments in the experimental and theoretical determination of the polarizabilities of simple atoms and molecules. Polarizability values (related to the “quadratic Stark effect”) are accurately known for the noble gas atoms and for hydrogen, in theory, but the remainder of the periodic table has proven much more difficult to deal with, both theoretically and experimentally. The static electric dipole polarizability of the ground-state hydrogen atom is almost exactly 4.5a30, where a0 is the Bohr radius. Across rows of the periodic table, polarizabilities range from hundreds (of a30 units) for the alkali metal atoms generally monotonically down to a few for noble gas atoms. Excited atoms have much larger polarizabilities; recent polarizability measurements for atoms in Rydberg orbits have yielded values on the order of 1010a30. Further research on molecular polarizabilities can help in the determination of polarizability anisotropies whether through state selection or with beams of different temperatures. Supersonic molecular beams are found to have low internal energies, and the internal energy can be controlled somewhat in “seeded” beams.

Electric Dipole Polarizability Measurements

Publisher Summary This chapter discusses the perturbation and nonperturbation methods of calculating atomic polarizabilities and shielding factors. Shielding factors are of considerable specialized interest because of the role they play in the determination of nuclear properties obtained from atomic spectroscopy experiments. Atomic and molecular polarizabilities, however, are of general interest because they appear as parameters in a large variety of atomic, molecular, and condensed matter properties. The most accurate polarizabilities available currently are determined from bulk measurements of a dielectric constant or refractive index for a gas of atoms or molecules. The determination of a dielectric constant is accomplished by measuring a capacitance change with and without the gas present. The dynamic polarizability corresponding to the frequency of the radiation can be obtained by replacing the molar polarization in the formula with the molar refraction. A permanent electric dipole moment would tend to cancel some of the deflection of the molecular beam that is observed for an induced moment alone, leading to the underestimation of the induced polarizability.

Measurements of the dc electric dipole polarizabilities of the alkali dimer molecules, homonuclear and heteronuclear

The average static (dc) electric dipole polarizabilities of the NaK and KCs heteronuclear alkali dimers have been measured, and those of the homonuclear molecules remeasured using molecular beam deflection in an inhomogeneous electric field. A congruent magnetic field enabled removal of the monomer constituents of the beam. The resulting deflection curves reflect both the permanent electric dipole force (for the heteronuclear dimers only), and the induced (polarizability) dipole force. It is assumed that the molecular constituents of the beam possess modified Maxwell–Boltzmann velocity and rotational state distributions. A Mach number is introduced to describe the sonic beam properties. The data analysis consists of a two‐parameter least squares best fit of the experimental deflection curves to computed ones, the parameters being the polarizability and the Mach number. Values of the permanent heteronuclear dipole moments are taken from the literature. The obtained static electric dipole polarizabilities i...

Measurements of the average electric dipole polarizabilities of the alkali dimers

The average electric dipole polarizabilities of the homonuclear alkali dimers have been measured in an electric deflection experiment. The molecular results are normalized to the corresponding atomic polarizabilities by comparing deflections of atomic and molecular alkali beams passing through an inhomogenous electrostatic field. The average polarizabilities in units of 10−24 cm3 are: Li2(990°K), 34±3; Na2(736°K), 30±3; K2(569°K), 61±5; Rb2(534°K), 68±7; Cs2(515°K), 91±7.

Polarizabilities of the alkali halide dimers. II

We have measured the average electric dipole polarizabilities of twenty alkali halide dimers, using a molecular beam electric deflection method. This is a continuation of the earlier measurements of five alkali halide dimers [R. Kremens et al., J. Chem. Phys. 81, 1676 (1984)]. We compare our measurements with a simple combination of bond (via a ‘‘spring’’ model) and effective ionic polarizabilities, using literature values for the required molecular constants. Agreement between our measured and calculated values is reasonable, in most cases, considering the relative crudeness of the model.

Atomic Beam E‐H Gradient Spectrometer

A novel atomic beam magnetic substate selector is described. A potential difference is applied to the insulated pole faces of an inhomogeneous magnet. The resulting E and H fields are then approximately congruent throughout the gap region. A beam atom experiences forces due to its effective magnetic moment and induced electric moment which can be made to balance for particular magnetic substates, independent of the atomic velocity. State‐selected beams of reasonable intensity and purity can thus be obtained.

Measurements of the electric dipole polarizabilities of the alkali halide dimers

We report the first measurements of the average electric dipole polarizabilities of five alkali halide dimers. A combined monomer‐dimer molecular beam deflection pattern in an inhomogeneous electric field is subject to an appropriate computational analysis to extract the polarizabilities. A simple combination of bond and effective ionic models to estimate the polarizabilities gives reasonably good agreement with the measured values. The values are, in units of 10−24 cm2, (KF)2:25.3±3.2; (KCl)2:28.6±3.0; (RbCl)2:43.4±4.2; (CsCl)2:36.6±5.0; (CsF)2:21.2±2.6.

Physics and New York City

When I was approached by the editors of Physics in Perspective to prepare an article on New York City for The Physical Tourist section, I was happy to do so. I have been a New Yorker all my life, except for short-term stays elsewhere on sabbatical leaves and other visits. My professional life developed in New York, and I married and raised my family in New York and its environs. Accordingly, writing such an article seemed a natural thing to do. About halfway through its preparation, however, the attack on the World Trade Center took place. From my apartment house I watched as the South Tower collapsed. Writing about New York and the role it has played in the history of physics in the United States and the world has now taken on a very different meaning.

Bethe's contributions to atomic and molecular physics

We discuss the contributions of Hans A Bethe to the fields of atomic, molecular and optical physics. Those contributions are seminal to these still vibrant major areas.

Total Cross Sections for the Scattering of Low-Energy Electrons by Excited Sodium Atoms

Preliminary values of the total scattering cross section of electrons on 3P3/2 sodium atoms have been measured at 1.0, 2.0, and 3.0 eV by an atomic double-recoil method. The atoms are excited by a single-mode tunable dye laser. The atomic recoil due to resonant photon interactions is used to spatially separate the excited atoms and to determine the fraction of excited atoms. Standard recoil techniques are used to determine the total cross sections. The results are compared with close-coupling calculations.