46 research outputs found
Manipulating Rydberg atoms close to surfaces at cryogenic temperatures
Helium atoms in Rydberg states have been manipulated coherently with
microwave radiation pulses near a gold surface and near a superconducting NbTiN
surface at a temperature of . The experiments were carried out with
a skimmed supersonic beam of metastable helium atoms excited with laser radiation to
Rydberg levels with principal quantum number between and . The
separation between the cold surface and the center of the collimated beam is
adjustable down to . Short-lived Rydberg levels
were coherently transferred to the long-lived state to avoid
radiative decay of the Rydberg atoms between the photoexcitation region and the
region above the cold surfaces. Further coherent manipulation of the
Rydberg levels with pulsed microwave radiation above the surfaces
enabled measurements of stray electric fields and allowed us to study the
decoherence of the atomic ensemble. Adsorption of residual gas onto the
surfaces and the resulting slow build-up of stray fields was minimized by
controlling the temperature of the surface and monitoring the partial pressures
of HO, N, O and CO in the experimental chamber during the
cool-down. Compensation of the stray electric fields to levels below was achieved over a region of along the
beam-propagation direction which, for the beam
velocity, implies the possibility to preserve the coherence of the atomic
sample for several microseconds above the cold surfaces.Comment: 12 pages, 10 figure
The Role of Nebulizer Gas Flow in Electrosonic Spray Ionization (ESSI)
In this work, we investigated the role of the nebulizer gas flow in electrosonic spray ionization (ESSI), by systematically studying the relation between the flow and the ion signals of proteins, such as cytochrome c and holomyoglobin using ESSI-mass spectrometry (MS). When a neutral solution was delivered with a small sample flow rate (≤5μL/min), no obvious transition from electrospray ionization (ESI) to ESSI was found as the gas velocity varies from subsonic to supersonic speed. Droplets mostly experienced acceleration instead of breakup by the high-speed nebulizer gas. On the contrary, using particular experimental conditions, such as an acidic solution or high sample flow rate (≥200μL/min), more folded protein ions appear to be kept in droplets of diminishing size due to breakup by the high-speed nebulizer gas in ESSI compared with ESI. Theoretical analyses and numerical simulations were also performed to explain the observed phenomena. These systematic studies clarify the ionization mechanism of ESSI and provide valuable insight for optimizing ESSI and other popular pneumatically assisted electrospray ionization methods for future application
Observation of enhanced rate coefficients in the H + H H + H reaction at low collision energies
The energy dependence of the rate coefficient of the H reaction has been measured in the range of
collision energies between K and
mK. A clear deviation of the rate coefficient from the value expected on the
basis of the classical Langevin-capture behavior has been observed at collision
energies below K, which is attributed to the joint
effects of the ion-quadrupole and Coriolis interactions in collisions involving
ortho-H molecules in the rotational level, which make up 75% of the
population of the neutral H molecules in the experiments. The experimental
results are compared to very recent predictions by Dashevskaya, Litvin, Nikitin
and Troe (J. Chem. Phys., in press), with which they are in agreement.Comment: 14 pages, 3 figure
New method to study ion-molecule reactions at low temperatures and application to the H + H H + H reaction
Studies of ion-molecule reactions at low temperatures are difficult because
stray electric fields in the reaction volume affect the kinetic energy of
charged reaction partners. We describe a new experimental approach to study
ion-molecule reactions at low temperatures and present, as example, a
measurement of the
reaction with the ion prepared in a single rovibrational state at
collision energies in the range -60 K. To reach such
low collision energies, we use a merged-beam approach and observe the reaction
within the orbit of a Rydberg electron, which shields the ions from stray
fields. The first beam is a supersonic beam of pure ground-state H
molecules and the second is a supersonic beam of H molecules excited to
Rydberg-Stark states of principal quantum number selected in the range
20-40. Initially, the two beams propagate along axes separated by an angle of
10. To merge the two beams, the Rydberg molecules in the latter beam
are deflected using a surface-electrode Rydberg-Stark deflector. The collision
energies of the merged beams are determined by measuring the velocity
distributions of the two beams and they are adjusted by changing the
temperature of the pulsed valve used to generate the ground-state
beam and by adapting the electric-potential functions to the electrodes of the
deflector. The collision energy is varied down to below K, i.e., below meV, with an energy resolution of 100
eV. We demonstrate that the Rydberg electron acts as a spectator and does
not affect the cross sections, which are found to closely follow a
classical-Langevin-capture model in the collision-energy range investigated.
Because all neutral atoms and molecules can be excited to Rydberg states, this
method of studyingComment: 39 pages, 10 figure
Experimental study of the ion-molecule reaction H2+ + H2 → H3+ + H at low collision energies
We present a new method to study ion-molecule reactions at low temperatures or low collision energies and illustrate its application to the study of the H2+ + H2 → H3+ + H reaction.ISSN:1742-6588ISSN:1742-659
Deceleration and trapping of a fast supersonic beam of metastable helium atoms with a 44-electrode chip decelerator
ISSN:1094-1622ISSN:0556-2791ISSN:1050-294
Surface-electrode decelerator and deflector for Rydberg atoms and molecules
ISSN:1094-1622ISSN:0556-2791ISSN:1050-294