The history of molecular beams since the invention of molecular beam magnetic resonance is discussed. Rabi`s 1937 theoretical paper on resonance transitions led Rabi, Zacharias, Millman and Kusch to measure various nuclear magnetic moments by magnetic resonance. Kellogg, Rabi, Ramsey and Zacharias found a multiple line radio frequency spectrum in H{sub 2}, D{sub 2}, and HD which enabled them to measure not only the nuclear magnetic moments but also internal molecular interactions including that of the deuteron electric quadrupole moment. The method was successfully extended to atoms. In 1947 Nafe, Nelson and Rabi found that the observed hyperfine separations in atomic hydrogen and deuterium differed from theoretical predictions and Lamb and Retherford soon thereafter observed the large Lamb shift in the atomic fine structures; these two discoveries were the principal incentives for the development of QED, which was confirmed by Kusch`s measurement of the electron magnetic moment. Ramsey`s separated oscillatory field method increased the accuracy and frequency range of the resonance method and provided the basis for accurate atomic clocks. Townes and his associates used a molecular beam for the first Maser as did Goldenberg, Klepper and Ramsey for the atomic hydrogen maser. Many nuclear, atomic and molecular properties havemore » been measured with the molecular beam magnetic resonance. Van der Waal`s molecules and highly excited Rydberg atoms have been examined. Laser spectroscopy has been extensively studied with atomic beams and lasers have been used for state selection and excitation. Wieman and others used atomic beams to study parity and time reversal symmetry. Atomic beams have been slowed by laser cooling and Phillips and others have shown that the atoms can be cooled to about one micro-Kelvin, well below the Doppler limit. Collision experiments between two beams, often from jet sources, provided extensive and detailed information about molecular interactions.« less
The history of molecular beams since the invention of molecular beam magnetic resonance is discussed. Rabis 1937 theoretical paper on resonance transitions led Rabi, Zacharias, Millman and Kusch to measure various nuclear magnetic moments by magnetic resonance. Kellogg, Rabi, Ramsey and Zacharias found a multiple line radio frequency spectrum in H{sub 2}, D{sub 2}, and HD which enabled them to measure not only the nuclear magnetic moments but also internal molecular interactions including that of the deuteron electric quadrupole moment. The method was successfully extended to atoms. In 1947 Nafe, Nelson and Rabi found that the observed hyperfine separations in atomic hydrogen and deuterium differed from theoretical predictions and Lamb and Retherford soon thereafter observed the large Lamb shift in the atomic fine structures; these two discoveries were the principal incentives for the development of QED, which was confirmed by Kuschs measurement of the electron magnetic moment. Ramseys separated oscillatory field method increased the accuracy and frequency range of the resonance method and provided the basis for accurate atomic clocks. Townes and his associates used a molecular beam for the first Maser as did Goldenberg, Klepper and Ramsey for the atomic hydrogen maser. Many nuclear, atomic and molecular properties havemore » been measured with the molecular beam magnetic resonance. Van der Waals molecules and highly excited Rydberg atoms have been examined. Laser spectroscopy has been extensively studied with atomic beams and lasers have been used for state selection and excitation. Wieman and others used atomic beams to study parity and time reversal symmetry. Atomic beams have been slowed by laser cooling and Phillips and others have shown that the atoms can be cooled to about one micro-Kelvin, well below the Doppler limit. Collision experiments between two beams, often from jet sources, provided extensive and detailed information about molecular interactions.« less
Summary Molecular beams are beams of molecules (which may be single atoms) travelling through vacuum at thermal velocities. They have been used to explore many properties of atoms and molecules, chiefly through their deflection in magnetic and electric inhomogeneous fields. Atomic beams first clearly established the phenomenon of space quantization, which means that the magnetic (or electric) energy of an atomic system in a given field can have only certain discrete values, and is not a continuum as classical physics supposed. Transitions between those energy states can be induced by radio-frequency fields; sharp resonances are observed and can be used to get accurate values of atomic and nuclear constants or to provide accurate frequency standards ('atomic clocks'). Molecular beams have also been used to test de Broglie's surmise that beams of particles should show wave properties (diffraction), to study collisions between molecules, and to supply spectroscopic sources in which the line broadening by Doppler effect is greatly reduced.
Abstract Over the past century, the molecular beam methods pioneered by Otto Stern have advanced our knowledge and understanding of the world enormously. Stern and his colleagues used these new techniques to measure the magnetic dipole moments of fundamental particles with results that challenged the prevailing ideas in fundamental physics at that time. Similarly, recent measurements of fundamental electric dipole moments challenge our present day theories of what lies beyond the Standard Model of particle physics. Measurements of the electron’s electric dipole moment (eEDM) rely on the techniques invented by Stern and later developed by Rabi and Ramsey. We give a brief review of this historical development and the current status of eEDM measurements. These experiments, and many others, are likely to benefit from ultracold molecules produced by laser cooling. We explain how laser cooling can be applied to molecules, review recent progress in this field, and outline some eagerly anticipated applications.
In this thesis three experiments with atomic hydrogen (H) at low temperatures T<1 K are presented. Experiments were carried out with two- (2D) and three-dimensional (3D) H gas, and with H atoms trapped in solid H2 matrix. The main focus of this work is on interatomic interactions, which have certain specific features in these three systems considered. A common feature is the very high density of atomic hydrogen, the systems are close to quantum degeneracy. Short range interactions in collisions between atoms are important in gaseous H. The system of H in H2 differ dramatically because atoms remain fixed in the H2 lattice and properties are governed by long-range interactions with the solid matrix and with H atoms. The main tools in our studies were the methods of magnetic resonance, with electron spin resonance (ESR) at 128 GHz being used as the principal detection method. For the first time in experiments with H in high magnetic fields and at low temperatures we combined ESR and NMR to perform electron-nuclear double resonance (ENDOR) as well as coherent two-photon spectroscopy. This allowed to distinguish between different types of interactions in the magnetic resonance spectra. Experiments with 2D H gas utilized the thermal compression method in homogeneous magnetic field, developed in our laboratory. In this work methods were developed for direct studies of 3D H at high density, and for creating high density samples of H in H2. We measured magnetic resonance line shifts due to collisions in the 2D and 3D H gases. First we observed that the cold collision shift in 2D H gas composed of atoms in a single hyperfine state is much smaller than predicted by the mean-field theory. This motivated us to carry out similar experiments with 3D H. In 3D H the cold collision shift was found to be an order of magnitude smaller for atoms in a single hyperfine state than that for a mixture of atoms in two different hyperfine states. The collisional shifts were found to be in fair agreement with the theory, which takes into account symmetrization of the wave functions of the colliding atoms. The origin of the small shift in the 2D H composed of single hyperfine state atoms is not yet understood. The measurement of the shift in 3D H provides experimental determination for the difference of the scattering lengths of ground state atoms. The experiment with H atoms captured in H2 matrix at temperatures below 1 K originated from our work with H gas. We found out that samples of H in H2 were formed during recombination of gas phase H, enabling sample preparation at temperatures below 0.5 K. Alternatively, we created the samples by electron impact dissociation of H2 molecules in situ in the solid. By the latter method we reached highest densities of H atoms reported so far, 3.5(5)x1019 cm-3. The H atoms were found to be stable for weeks at temperatures below 0.5 K. The observation of dipolar interaction effects provides a verification for the density measurement. Our results point to two different sites for H atoms in H2 lattice. The steady-state nuclear polarizations of the atoms were found to be non-thermal. The possibility for further increase of the impurity H density is considered. At higher densities and lower temperatures it might be possible to observe phenomena related to quantum degeneracy in solid.
Polarized atomic beam sources have been in operation for many years to produce either nuclear polarized atomic hydrogen or deuterium beams. In recent experiments, such a source was used to polarize both isotopes independently at the same time. By recombination of the atoms, hydrogen-deuterium molecules with all possible nuclear spin combinations can be created. Those spin isomers are useful for further applications, like precision spectroscopy, as polarized targets for laser-particle acceleration, polarized fuel for fusion reactors, or as an option for future measurements of electric dipole moments.
During the last years some interesting experimental results have been reported for experiments in N2O, NO, NO dimer, H2, Toluene and BaFCH3 cluster. The main result consists in the observation of molecular beam depletion when the molecules of a pulsed beam interact with a static electric or magnetic field and an oscillating field (RF). In these cases, and as a main difference, instead of using four fields as in the original technique developed by I.I. Rabi and others, only two fields, those which configure the resonant unit, are used. That is, without using the nonhomogeneous magnetic fields. The depletion explanation for I.I. Rabi and others is based in the interaction between the molecular electric or magnetic dipole moment and the non-homogeneous fields. But, obviously, the change in the molecules trajectories observed on these new experiments has to be explained without considering the force provided by the field gradient because it happens without using non-homogeneous fields. In this paper a theoretical way for the explanation of these new experimental results is presented. One important point emerges as a result of this development, namely, the existence of an, until now unknown, spin-dependent force which would be responsible of the aforementioned deviation of the molecules.
Slowing down atoms using laser cooling, together with techniques like magnetic trapping and evaporative cooling, has led to numerous exciting results over the last decade [1], with the realization of Bose-Einstein condensation as the most spectacular achievement [2]. Laser-cooling schemes are applicable to atoms since closed multilevel systems can be realized and many consecutive absorptionemission cycles can be induced. This leads to a significant momentum transfer from the photons of the laser to the atom, resulting in a change of the velocity of the atom. There currently is a great interest in producing cold molecules for the study of cold molecule-molecule collisions, molecular quantum collective effects, Doppler-free spectroscopy, frequency standards, as well as many other applications already realized for atoms [3]. Slowing down of neutral molecules, a prerequisite for being able to trap them, has proven to be considerably more difficult to be achieved, however. The above-mentioned laser-cooling scheme cannot be applied to slow down molecules as no simple closed-level systems can be found; the unavoidable off-resonant radiative decay of molecules from the excited state to other vibrational levels in the electronic ground state hampers efficient momentum transfer [4]. Once molecules are present at sufficiently low kinetic energies, below a fraction of a cm21, they can be trapped in various ways. Trapping of neutral molecules in inhomogeneous magnetic [3] and electric fields [5] and trapping based on the use of evanescent fields close to the dielectricvacuum interface have been proposed [6]. It has also been suggested that extremely high laser powers might be used to induce a dipole moment in polarizable molecules, leading to trapping of these molecules in the laser beam [7]. Other methods to produce slow molecules have been put forward and have recently been successfully applied to produce the first samples of trapped molecules. By injecting molecules in a cold buffer gas, sufficiently low kinetic energies of the injected molecules can be obtained after thermalization that they can subsequently be trapped in an inhomogeneous magnetic field. This has recently been demonstrated for CaH injected in 3He buffer gas at temperatures of around 0.3 K [8]. Associative collisions between ultracold trapped atoms [9] have proven to be