CONTENTS 1. Introduction 4829 2. Historical Overview 4829 3. Stark and Zeeman Effect 4831 3.1. Introduction 4831 3.2. General Formalism 4832 3.3. Stark Effect 4833 3.3.1. Matrix Elements of H Stark 4833 3.3.2. Matrix Elements in a Basis of Symmetrized Wave Functions 4833 3.3.3. Diatomic Molecules and (A)symmetric Tops 4833 3.3.4. HCl, OH, and YbF 4834 3.3.5. ND 3 , H 2 CO, and HDO 4835 3.3.6. Candidate Molecules for Stark Deceleration 4835 3.4. Zeeman Effect 4836 3.4.1. Matrix Elements of H Zeeman in Atoms 4836 3.4.3. The Zeeman Effect of OH (X 2 Π i ) and 16 O 2 (X 3 Σ g − ) 4837 3.4.4. Candidate Molecules for Zeeman Deceleration 4838 4. Deflection and Focusing of Molecular Beams 4838 4.1. Multipole Expansion of the Electric Field in Two Dimensions 4839 4.2. Deflection Fields 4839 4.3. Focusing Low-Field Seekers 4840 4.4. Guiding Low-Field Seekers 4841 4.5. Focusing High-Field Seekers 4842 4.6. Guiding High-Field Seekers 4843 5. Deceleration of Neutral Molecules 4843 5.1.

A pulsed beam of ground state OH radicals is slowed down using a Stark decelerator and is subsequently loaded into an electrostatic trap. Characterization of the molecular beam production, deceleration, and trap loading process is performed via laser induced fluorescence detection inside the quadrupole trap. Depending on the details of the trap loading sequence, typically 10(5) OH (X2Pi(3/2),J=3/2) radicals are trapped at a density of around 10(7) cm(-3) and at temperatures in the 50-500 mK range. The 1/e trap lifetime is around 1.0 s.

The deceleration of beams of neutral particles possessing an electron spin with time-dependent inhomogeneous magnetic fields is demonstrated experimentally. Half the kinetic energy of a velocity-selected part of a pulsed supersonic beam of hydrogen atoms in the ground state is removed using six pulsed magnetic field stages.

Neutral molecules, isolated in the gas phase, can be prepared in a long-lived excited state and stored in a trap. The long observation time afforded by the trap can then be exploited to measure the radiative lifetime of this state by monitoring the temporal decay of the population in the trap. This method is demonstrated here and used to benchmark the Einstein A coefficients in the Meinel system of OH. A pulsed beam of vibrationally excited OH radicals is Stark decelerated and loaded into an electrostatic quadrupole trap. The radiative lifetime of the upper Lamda-doublet component of the Chi2Pi3/2, v=1, J=3/2 level is determined as 59.0+/-2.0 ms, in good agreement with the calculated value of 58.0+/-1.0 ms.

The concept of phase stability in a Stark decelerator ensures that polar molecules can be accelerated, guided, or decelerated without loss; molecules within a certain position and velocity interval are kept together throughout the deceleration process. In this paper the influence of the transverse motion on phase stability in a Stark decelerator is investigated. For typical deceleration experiments-i.e., for high values of the phase angle 0 -the transverse motion considerably enhances the region in phase space for which phase stable deceleration occurs. For low values of 0 , however, the transverse motion reduces the acceptance of a Stark decelerator and unstable regions in phase space appear. These effects are quantitatively explained in terms of a coupling between the longitudinal and transverse motion. The predicted longitudinal acceptance of a Stark decelerator is verified by measurements on a beam of OH ͑X 2 ⌸ 3/2 , J =3/2͒ radicals passing through a Stark decelerator.

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Optical pumping by blackbody radiation is a feature shared by all polar molecules and fundamentally limits the time that these molecules can be kept in a single quantum state in a trap. To demonstrate and quantify this, we have monitored the optical pumping of electrostatically trapped OH and OD radicals by room-temperature blackbody radiation. Transfer of these molecules to rotationally excited states by blackbody radiation at 295 K limits the 1=e trapping time for OH and OD in the X 2 3=2 , v 00 0, J 00 3=2f state to 2.8 and 7.1 s, respectively. DOI: 10.1103/PhysRevLett.98.133001 PACS numbers: 33.80.Ps, 33.55.Be, 44.40.+a In his 1917 paper Einstein showed [1] that even in the absence of collisions the velocity distribution of a molecular gas takes on a Maxwellian distribution due to the momentum transfer that takes place in the absorption and emission of blackbody radiation. The absorbed and emitted photons optically pump the rotational and vibrational transitions, resulting in thermal distributions over the available states. The rotational temperature of the CN molecule in interstellar space [2], for example, is the result of optical pumping by the cosmic microwave background-radiation [3].The influence of blackbody radiation on atoms and molecules is in general small and it is rare that it can be observed directly in laboratory experiments. However, in a number of cases the interaction with blackbody radiation is experimentally observable and important. The first dynamical effects of blackbody radiation on the population of atomic levels were noticed when studying the lifetime of highly excited Rydberg states in atoms [4]. Atoms in these states can have dipole moments of thousands of Debye, and have sufficient spectral overlap with the spectrum of roomtemperature blackbody radiation. The excitation (and ionization) rates can be on the order of 1000 s ÿ1 , implying that the effect can already be observed on a s time scale.The excitation rates in ground state atoms and molecules are generally much lower, and therefore require a longer interaction time to be observed. Only with the development of ion traps, together with a sufficient reduction of collisional energy exchange (i.e., a good vacuum at room temperature), could the photodissociation of molecular ions and clusters by blackbody radiation be directly observed [5,6]. Ions in storage rings are also trapped long enough for the interaction with blackbody radiation to be noticeable [7].The effect of blackbody radiation on neutral molecules in a trap has until now been left experimentally unexplored, partly because the conditions to observe the effect were not met, and partly because the importance of this effect was not always realized. Polar molecules generally have strong vibrational and/or rotational transitions in the infrared region of the spectrum. As a result they can relatively easily be optically pumped by room-temperature blackbody radiation, and this fundamentally limits the time that these molecules can be kept in a single quantum state in ro...

Dense samples of cold Rydberg atoms have previously been observed to spontaneously evolve to a plasma, despite the fact that each atom may be bound by as much as 100 cm −1 . Initially, ionization is caused by blackbody photoionization and Rydberg-Rydberg collisions. After the first electrons leave the interaction region, the net positive charge traps subsequent electrons. As a result, rapid ionization starts to occur after 1 s caused by electron-Rydberg collisions. The resulting cold plasma expands slowly and persists for tens of microseconds. While the initial report on this process identified the key issues described above, it failed to resolve one key aspect of the evolution process. Specifically, redistribution of population to Rydberg states other than the one initially populated was not observed, a necessary mechanism to maintain the energy balance in the system. Here we report new and expanded observations showing such redistribution and confirming theoretical predictions concerning the evolution to a plasma. These measurements also indicate that, for high n states of purely cold Rydberg samples, the initial ionization process which leads to electron trapping is one involving the interactions between Rydberg atoms.