We report on the Stark deceleration and electrostatic trapping of ¹⁴NH (a¹Δ) radicals. In the trap, the molecules are excited on the spin-forbidden A³∏ <- a¹Δ transition and detected via their subsequent fluorescence to the X³∑⁻ ground state. The 1/e trapping time is 1.4 ± 0.1 s, from which a lower limit of 2.7 s for the radiative lifetime of the a¹Δ, v=0, ,J=2 state is deduced. The spectral profile of the molecules in the trapping field is measured to probe their spatial distribution. Electrostatic trapping of metastable NH followed by optical pumping of the trapped molecules to the electronic ground state is an important step towards accumulation of these radicals in a magnetic trap
The level of control that one has over neutral molecules in beams dictates their possible applications. Here we experimentally demonstrate that state-selected, neutral molecules can be kept together in a few mm long packet for a distance of over one mile. This is accomplished in a circular arrangement of 40 straight electrostatic hexapoles through which the molecules propagate over 1000 times. Up to 19 packets of molecules have simultaneously been stored in this ring structure. This brings the realization of a molecular low-energy collider within reach.
We study collisions between neutral, deuterated ammonia molecules (ND 3 ) stored in a 50 cm diameter synchrotron and argon atoms in copropagating supersonic beams. The advantages of using a synchrotron in collision studies are twofold: (i) By storing ammonia molecules many round-trips, the sensitivity to collisions is greatly enhanced; (ii) the collision partners move in the same direction as the stored molecules, resulting in low collision energies. We tune the collision energy in three different ways: by varying the velocity of the stored ammonia packets, by varying the temperature of the pulsed valve that releases the argon atoms, and by varying the timing between the supersonic argon beam and the stored ammonia packets. These give consistent results. We determine the relative, total, integrated cross section for ND 3 þ Ar collisions in the energy range of 40-140 cm −1 , with a resolution of 5-10 cm −1 and an uncertainty of 7%-15%. Our measurements are in good agreement with theoretical scattering calculations. DOI: 10.1103/PhysRevLett.120.033402 The crossed molecular beam technique, pioneered by Herschbach and Lee, has yielded a detailed understanding of how molecules interact and react [1,2]. Until recently, these crossed molecular beam studies were limited by the velocities of the molecular beams to collision energies above a few hundred cm −1 (1 cm −1 ≃ 1.4 K). Over the past years, however, a number of ingenious methods [3][4][5] have been developed to study collisions in the cold regime. These advances are important for several reasons. First, the temperatures of interstellar clouds are typically between 10 and 100 K; collision data of simple molecules at low temperatures are thus highly relevant for understanding the chemistry in these clouds [6]. Furthermore, quantum effects become important at low temperatures, where few partial waves contribute and the de Broglie wavelength associated with the relative velocity becomes comparable to or larger than the intermolecular distances. Of particular interest are resonances of the collision cross section as a function of the collision energy [7][8][9][10]. The position and shape of these resonances are very sensitive to the exact shape of the PES and thus serve as precise tests of our understanding of intermolecular forces.The ability to control the velocity of molecules using time-varying electric fields has allowed studies of inelastic collisions of OH and NO molecules with rare gas atoms at low collision energies [11][12][13][14]. Using cryogenically cooled beams under a small (and variable) crossing angle, inelastic collisions of O 2 and CO with H 2 and helium at energies between 5 and 30 K have been studied [15]. Even lower temperatures can be obtained by using magnetic or electric guides to merge two molecular beams into a single beam. This technique has been used to study Penning ionization reactions of various atoms and molecules with metastable helium [16][17][18][19] and collisions between ground state hydrogen molecules and hydrogen molecules in ...
We present a synchrotron for polar molecules consisting of 40 straight hexapoles arranged in a circle with a 50 cm diameter. The mechanical design and alignment procedure as well as the trigger scheme used to switch the voltages applied to the hexapoles is described in detail. The stability of the synchrotron is demonstrated by measurements in which multiple packets are stored for over 13 seconds, during which they have completed over 1000 round trips and traveled a distance of over one mile. Furthermore, we demonstrate the simultaneous trapping of 26 packets; 13 revolving clock-wise and 13 counter clock-wise in the ring that are injected into the ring by two Stark decelerator beamlines. We discuss the opportunities for using the synchrotron as low-energy collider.
Please be advised that this information was generated on 2018-05-09 and may be subject to change.PHYSICAL REVIEW A 87, 043425 (2013) Resonant excitation of trapped molecules in a molecular synchrotron We characterize a synchrotron for polar molecules that consists of forty straight hexapoles arranged in a circle. By modulating either the voltages or the duration of the high-voltage pulses that are applied to the hexapoles, we shake the transverse and longitudinal well. If the frequency of the modulation matches a characteristic frequency of a stored molecule, the amplitude of the motion is resonantly excited, leading to a decrease in the number of molecules that are stored. From this, we determine the longitudinal, vertical, and radial frequencies that characterize the motion of the molecules inside the synchrotron and obtain knowledge about the couplings between the longitidinal and transverse motion. The measured frequencies are in good agreement with those obtained from three-dimensional trajectory calculations.
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