Physical Review A

Accumulating NH radicals in a magnetic trap

Sebastiaan Y. T. van de Meerakker, Rienk T. Jongma, Hendrick L. Bethlem, Gerard Meijer

Published Sep 13, 2001• 73 citations

Abstract

We propose a scheme to accumulate fermionic or bosonic NH radicals ${(}^{14}\mathrm{NH}$ or ${}^{15}\mathrm{NH},$ respectively) in a magnetic trap in order to increase phase-space density. NH molecules prepared in a long-lived metastable state that exhibits a large Stark effect can be brought to a standstill using Stark deceleration. By applying an intense laser field, the NH radicals can then be forced to spontaneously decay to the electronic ground state. In the ground state the NH molecules are no longer sensitive to electric fields but show a significant Zeeman effect instead, enabling confinement and reloading of ground-state molecules in a magnetic trap.

DOI: 10.1103/physreva.64.041401

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Deceleration and trapping of polyatomic molecules

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Physical Review A

Accumulating NH radicals in a magnetic trap

Sebastiaan Y. T. van de Meerakker, Rienk T. Jongma, Hendrick L. Bethlem, Gerard Meijer

Published Sep 13, 2001• 73 citations

Publisher

Abstract

We propose a scheme to accumulate fermionic or bosonic NH radicals

{(}^{14}\mathrm{NH}

{}^{15}\mathrm{NH},

respectively) in a magnetic trap in order to increase phase-space density. NH molecules prepared in a long-lived metastable state that exhibits a large Stark effect can be brought to a standstill using Stark deceleration. By applying an intense laser field, the NH radicals can then be forced to spontaneously decay to the electronic ground state. In the ground state the NH molecules are no longer sensitive to electric fields but show a significant Zeeman effect instead, enabling confinement and reloading of ground-state molecules in a magnetic trap.

DOI: 10.1103/physreva.64.041401

Related papers

Production and deceleration of a pulsed beam of metastable NH (a1Δ) radicals

Sebastiaan Y. T. van de Meerakker, Irena Labazan, Steven Hoekstra +2 more

We report on the production of a pulsed molecular beam of metastable NH ( $a ^1Δ$ ) radicals and present first results on the Stark deceleration of the NH ( $a ^1Δ, J=2, MΩ=-4$ ) radicals from 550 m/s to 330 m/s. The decelerated molecules are excited on the spin-forbidden $A ^3Π\leftarrow a ^1Δ$ transition, and detected via their subsequent spontaneous fluorescence to the $X ^3Σ^{-}, v"=0$ ground-state. These experiments demonstrate the feasibility of our recently proposed scheme [Phys. Rev. A 64 (2001) 041401] to accumulate ground-state NH radicals in a magnetic trap.We report on the production of a pulsed molecular beam of metastable NH ($a ^1Δ$) radicals and present first results on the Stark deceleration of the NH ($a ^1Δ, J=2, MΩ=-4$) radicals from 550 m/s to 330 m/s. The decelerated molecules are excited on the spin-forbidden $A ^3Π\leftarrow a ^1Δ$ transition, and detected via their subsequent spontaneous fluorescence to the $X ^3Σ^{-}, v"=0$ ground-state. These experiments demonstrate the feasibility of our recently proposed scheme [Phys. Rev. A 64 (2001) 041401] to accumulate ground-state NH radicals in a magnetic trap.

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Electrostatic trapping of metastable NH molecules

Steven Hoekstra, Markus Metsälä, Peter C. Zieger +4 more

We report on the Stark deceleration and electrostatic trapping of $^{14}\text{N}\text{H}$ $(a^{1}\ensuremath{\Delta})$ radicals. In the trap, the molecules are excited on the spin-forbidden $A^{3}\ensuremath{\Pi}\ensuremath{\leftarrow}a^{1}\ensuremath{\Delta}$ transition and detected via their subsequent fluorescence to the $X{^{3}\ensuremath{\Sigma}}^{\ensuremath{-}}$ ground state. The $1∕e$ trapping time is $1.4\ifmmode\pm\else\textpm\fi{}0.1\text{ }\text{s}$, from which a lower limit of 2.7 s for the radiative lifetime of the $a^{1}\ensuremath{\Delta}$, $v=0$ , $J=2$ 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 toward accumulation of these radicals in a magnetic trap.We report on the Stark deceleration and electrostatic trapping of $^{14}\text{N}\text{H}$ $(a^{1}\ensuremath{\Delta})$ radicals. In the trap, the molecules are excited on the spin-forbidden $A^{3}\ensuremath{\Pi}\ensuremath{\leftarrow}a^{1}\ensuremath{\Delta}$ transition and detected via their subsequent fluorescence to the $X{^{3}\ensuremath{\Sigma}}^{\ensuremath{-}}$ ground state. The $1∕e$ trapping time is $1.4\ifmmode\pm\else\textpm\fi{}0.1\text{ }\text{s}$, from which a lower limit of 2.7 s for the radiative lifetime of the $a^{1}\ensuremath{\Delta}$, $v=0$, $J=2$ 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 toward accumulation of these radicals in a magnetic trap.

arXiv:0709.3212Physical Review ADec 27, 200770 citations

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Sebastiaan Y. T. van de Meerakker, Boris G. Sartakov, Allard P. Mosk +2 more

We here report on the optical pumping of both ${}^{14}\mathrm{NH}$ and ${}^{15}\mathrm{NH}$ radicals from the metastable $a{}^{1}\ensuremath{\Delta}$ state into the $X{}^{3}{\ensuremath{\Sigma}}^{\ensuremath{-}}$ ground state in a molecular beam experiment. By inducing the hitherto unobserved spin-forbidden $A{}^{3}\ensuremath{\Pi}\ensuremath{\leftarrow}a{}^{1}\ensuremath{\Delta}$ transition, followed by spontaneous emission to the $X{}^{3}{\ensuremath{\Sigma}}^{\ensuremath{-}}$ state, a unidirectional pathway for population transfer from the metastable state into the electronic ground state is obtained. The optical pumping scheme demonstrated here opens up the possibility to accumulate NH radicals in a magnetic or optical trap.We here report on the optical pumping of both ${}^{14}\mathrm{NH}$ and ${}^{15}\mathrm{NH}$ radicals from the metastable $a{}^{1}\ensuremath{\Delta}$ state into the $X{}^{3}{\ensuremath{\Sigma}}^{\ensuremath{-}}$ ground state in a molecular beam experiment. By inducing the hitherto unobserved spin-forbidden $A{}^{3}\ensuremath{\Pi}\ensuremath{\leftarrow}a{}^{1}\ensuremath{\Delta}$ transition, followed by spontaneous emission to the $X{}^{3}{\ensuremath{\Sigma}}^{\ensuremath{-}}$ state, a unidirectional pathway for population transfer from the metastable state into the electronic ground state is obtained. The optical pumping scheme demonstrated here opens up the possibility to accumulate NH radicals in a magnetic or optical trap.

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Deceleration and trapping of polyatomic molecules

Manish Vashishta

In this dissertation, substantial headway towards the Zeeman deceleration and magnetic trapping of methyl radicals, and AC Stark trapping of ammonia are presented. Notably, the first ever trapping of gaseous methyl radicals within a permanent magnetic trap is discussed in detail. Additionally, the use of a counter rotating nozzle to produce slow polyatomic molecular beam is discussed. The methyl radical is the smallest and most stable paramagnetic intermediate hydrocarbon species, and as such, the physicochemical properties of this species are of substantial interest to astrochemists and organic chemists alike. Methyl radical, being a paramagnetic molecule, is decelerated using an 85 coil Zeeman decelerator from 320 m/s to 60 m/s. Notably, the first ever trapping of methyl radicals in the gas phase inside a permanent magnetic trap is described here. The trapped radicals had a temperature of 200 mK, and a lifetime of greater than one second. Lastly, the collisional loss cross sections for the methyl radical with helium and argon are also reported. In addition to the magnetic trapping of the methyl radical, progress towards the trapping of polar molecules with microwave radiation is discussed in detail. A quality (abbr. Q) factor of 5 x 105 was achieved by cooling a Fabry Perot cavity with superconducting mirror surfaces to 3 K. Resulting from the large Q factor, the maximum electric field inside the cavity is 1 MV/m when a power input of 10 W is used. At this electric field, ammonia molecules travelling slower than 10 m/s can be successfully trapped. Additionally, the AC stark shift of ammonia molecules within the trap is reported as the first step towards their trapping. Lastly, a counter rotating nozzle was constructed based on the design presented by Strebel et al. at the University of Freiburg. The technical modifications presented in this thesis yielded an increase in the density of the molecular beam by two orders of magnitude, in comparison to the Freiburg design. This nozzle was used to decelerate acetone from 430 m/s to 110 m/s, and unlike the Stark and Zeeman decelerators, it can be used to decelerate any gaseous molecules.In this dissertation, substantial headway towards the Zeeman deceleration and magnetic trapping of methyl radicals, and AC Stark trapping of ammonia are presented. Notably, the first ever trapping of gaseous methyl radicals within a permanent magnetic trap is discussed in detail. Additionally, the use of a counter rotating nozzle to produce slow polyatomic molecular beam is discussed. The methyl radical is the smallest and most stable paramagnetic intermediate hydrocarbon species, and as such, the physicochemical properties of this species are of substantial interest to astrochemists and organic chemists alike. Methyl radical, being a paramagnetic molecule, is decelerated using an 85 coil Zeeman decelerator from 320 m/s to 60 m/s. Notably, the first ever trapping of methyl radicals in the gas phase inside a permanent magnetic trap is described here. The trapped radicals had a temperature of 200 mK, and a lifetime of greater than one second. Lastly, the collisional loss cross sections for the methyl radical with helium and argon are also reported. In addition to the magnetic trapping of the methyl radical, progress towards the trapping of polar molecules with microwave radiation is discussed in detail. A quality (abbr. Q) factor of 5 x 105 was achieved by cooling a Fabry Perot cavity with superconducting mirror surfaces to 3 K. Resulting from the large Q factor, the maximum electric field inside the cavity is 1 MV/m when a power input of 10 W is used. At this electric field, ammonia molecules travelling slower than 10 m/s can be successfully trapped. Additionally, the AC stark shift of ammonia molecules within the trap is reported as the first step towards their trapping. Lastly, a counter rotating nozzle was constructed based on the design presented by Strebel et al. at the University of Freiburg. The technical modifications presented in this thesis yielded an increase in the density of the molecular beam by two orders of magnitude, in comparison to the Freiburg design. This nozzle was used to decelerate acetone from 430 m/s to 110 m/s, and unlike the Stark and Zeeman decelerators, it can be used to decelerate any gaseous molecules.

Jan 1, 20200 citations

Magnetoelectrostatic Trapping of Ground State OH Molecules

Brian C. Sawyer, Benjamin Lev, Eric R. Hudson +4 more

We report magnetic confinement of neutral, ground state OH at a density of approximately 3 x 10(3) cm(-3) and temperature of approximately 30 mK. An adjustable electric field sufficiently large to polarize the OH is superimposed on the trap in various geometries, making an overall potential arising from both Zeeman and Stark effects. An effective molecular Hamiltonian is constructed, with Monte Carlo simulations accurately modeling the observed single-molecule dynamics in various trap configurations. Magnetic trapping of cold polar molecules under adjustable electric fields may enable study of low energy dipolar interactions.We report magnetic confinement of neutral, ground state OH at a density of approximately 3 x 10(3) cm(-3) and temperature of approximately 30 mK. An adjustable electric field sufficiently large to polarize the OH is superimposed on the trap in various geometries, making an overall potential arising from both Zeeman and Stark effects. An effective molecular Hamiltonian is constructed, with Monte Carlo simulations accurately modeling the observed single-molecule dynamics in various trap configurations. Magnetic trapping of cold polar molecules under adjustable electric fields may enable study of low energy dipolar interactions.

arXiv:physics/0702146Physical Review LettersJun 21, 2007164 citations

Magnetic Trapping and Zeeman Relaxation of NH ( X Σ−3 )

Wesley C. Campbell, Edem Tsikata, Hsin-I Lu +2 more

NH radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational, and rotational ground state NH molecules in collisions with $^{3}\mathrm{He}$ is measured to be $3.8\ifmmode\pm\else\textpm\fi{}1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\text{ }\text{ }{\mathrm{cm}}^{2}$ at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of $\ensuremath{\gamma}=7\ifmmode\times\else\texttimes\fi{}{10}^{4}$, in agreement with recent theory [R. V. Krems, H. R. Sadeghpour, A. Dalgarno, D. Zgid, J. K\l{}os, and G. Cha\l{}asi\ifmmode \acute{n}\else \'{n}\fi{}ski, Phys. Rev. A 68, 051401 (2003)].NH radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational, and rotational ground state NH molecules in collisions with $^{3}\mathrm{He}$ is measured to be $3.8\ifmmode\pm\else\textpm\fi{}1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\text{ }\text{ }{\mathrm{cm}}^{2}$ at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of $\ensuremath{\gamma}=7\ifmmode\times\else\texttimes\fi{}{10}^{4}$, in agreement with recent theory [R. V. Krems, H. R. Sadeghpour, A. Dalgarno, D. Zgid, J. K\l{}os, and G. Cha\l{}asi\ifmmode \acute{n}\else \'{n}\fi{}ski, Phys. Rev. A 68, 051401 (2003)].

arXiv:physics/0702071Physical Review LettersMay 25, 2007131 citations

We propose a scheme to accumulate fermionic or bosonic NH radicals

{(}^{14}\mathrm{NH}

{}^{15}\mathrm{NH},

We report on the production of a pulsed molecular beam of metastable NH (

a ^1Δ

) radicals and present first results on the Stark deceleration of the NH (

a ^1Δ, J=2, MΩ=-4

) radicals from 550 m/s to 330 m/s. The decelerated molecules are excited on the spin-forbidden

A ^3Π\leftarrow a ^1Δ

transition, and detected via their subsequent spontaneous fluorescence to the

X ^3Σ^{-}, v"=0

ground-state. These experiments demonstrate the feasibility of our recently proposed scheme [Phys. Rev. A 64 (2001) 041401] to accumulate ground-state NH radicals in a magnetic trap.

We report on the Stark deceleration and electrostatic trapping of

^{14}\text{N}\text{H}

$(a^{1}\ensuremath{\Delta})$ radicals. In the trap, the molecules are excited on the spin-forbidden $A^{3}\ensuremath{\Pi}\ensuremath{\leftarrow}a^{1}\ensuremath{\Delta}$ transition and detected via their subsequent fluorescence to the $X{^{3}\ensuremath{\Sigma}}^{\ensuremath{-}}$ ground state. The

1∕e

trapping time is $1.4\ifmmode\pm\else\textpm\fi{}0.1\text{ }\text{s}$, from which a lower limit of 2.7 s for the radiative lifetime of the $a^{1}\ensuremath{\Delta}$,

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 toward accumulation of these radicals in a magnetic trap.

We here report on the optical pumping of both

{}^{14}\mathrm{NH}

and

{}^{15}\mathrm{NH}

radicals from the metastable $a{}^{1}\ensuremath{\Delta}$ state into the $X{}^{3}{\ensuremath{\Sigma}}^{\ensuremath{-}}$ ground state in a molecular beam experiment. By inducing the hitherto unobserved spin-forbidden $A{}^{3}\ensuremath{\Pi}\ensuremath{\leftarrow}a{}^{1}\ensuremath{\Delta}$ transition, followed by spontaneous emission to the $X{}^{3}{\ensuremath{\Sigma}}^{\ensuremath{-}}$ state, a unidirectional pathway for population transfer from the metastable state into the electronic ground state is obtained. The optical pumping scheme demonstrated here opens up the possibility to accumulate NH radicals in a magnetic or optical trap.

^{3}\mathrm{He}

is measured to be $3.8\ifmmode\pm\else\textpm\fi{}1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\text{ }\text{ }{\mathrm{cm}}^{2}$ at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of $\ensuremath{\gamma}=7\ifmmode\times\else\texttimes\fi{}{10}^{4}$, in agreement with recent theory [R. V. Krems, H. R. Sadeghpour, A. Dalgarno, D. Zgid, J. K\l{}os, and G. Cha\l{}asi\ifmmode \acute{n}\else \'{n}\fi{}ski, Phys. Rev. A 68, 051401 (2003)].