arXiv:physics/0505039 · Physical Review Letters

Continuous Loading of an Electrostatic Trap for Polar Molecules

T. Rieger, T. Junglen, S. A. Rangwala, Pepijn W. H. Pinkse, Gerhard Rempe

Published Oct 18, 2005• 102 citations

Abstract

A continuously operated electrostatic trap for polar molecules is demonstrated. The trap has a volume of $\ensuremath{\approx}0.6\text{ }\text{ }{\mathrm{cm}}^{3}$ and holds molecules with a positive Stark shift. With deuterated ammonia from a quadrupole velocity filter, a trap density of $\ensuremath{\approx}{10}^{8}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ is achieved with an average lifetime of 130 ms and a motional temperature of $\ensuremath{\approx}300\text{ }\text{ }\mathrm{mK}$. The trap offers good starting conditions for high-precision measurements, and can be used as a first stage in cooling schemes for molecules and as a ``reaction vessel'' in cold chemistry.

DOI: 10.1103/physrevlett.95.173002

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arXiv:physics/0505039 · Physical Review Letters

Continuous Loading of an Electrostatic Trap for Polar Molecules

T. Rieger, T. Junglen, S. A. Rangwala, Pepijn W. H. Pinkse, Gerhard Rempe

Published Oct 18, 2005• 102 citations

arXiv HTML PDF

Abstract

A continuously operated electrostatic trap for polar molecules is demonstrated. The trap has a volume of

\ensuremath{\approx}0.6\text{ }\text{ }{\mathrm{cm}}^{3}

and holds molecules with a positive Stark shift. With deuterated ammonia from a quadrupole velocity filter, a trap density of

\ensuremath{\approx}{10}^{8}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}

is achieved with an average lifetime of 130 ms and a motional temperature of

\ensuremath{\approx}300\text{ }\text{ }\mathrm{mK}

. The trap offers good starting conditions for high-precision measurements, and can be used as a first stage in cooling schemes for molecules and as a ``reaction vessel'' in cold chemistry.

DOI: 10.1103/physrevlett.95.173002

Related papers

Continuous source of translationally cold dipolar molecules

S. A. Rangwala, T. Junglen, T. Rieger +2 more

The Stark interaction of polar molecules with an inhomogeneous electric field is exploited to select slow molecules from a room-temperature reservoir and guide them into an ultrahigh vacuum chamber. A linear electrostatic quadrupole with a curved section selects molecules with small transverse and longitudinal velocities. The source is tested with formaldehyde $({\mathrm{H}}_{2}\mathrm{CO})$ and deuterated ammonia $({\mathrm{ND}}_{3}).$ With ${\mathrm{H}}_{2}\mathrm{CO}$ a continuous flux is measured of $\ensuremath{\approx}{10}^{9}/\mathrm{s}$ and a longitudinal temperature of a few kelvin. The data are compared with the result of a Monte Carlo simulation.The Stark interaction of polar molecules with an inhomogeneous electric field is exploited to select slow molecules from a room-temperature reservoir and guide them into an ultrahigh vacuum chamber. A linear electrostatic quadrupole with a curved section selects molecules with small transverse and longitudinal velocities. The source is tested with formaldehyde $({\mathrm{H}}_{2}\mathrm{CO})$ and deuterated ammonia $({\mathrm{ND}}_{3}).$ With ${\mathrm{H}}_{2}\mathrm{CO}$ a continuous flux is measured of $\ensuremath{\approx}{10}^{9}/\mathrm{s}$ and a longitudinal temperature of a few kelvin. The data are compared with the result of a Monte Carlo simulation.

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We propose a novel optical-access opened electrostatic trap to study the Stark-potential evaporative cooling of polar molecules by using two charged disk electrodes with a central hole of radius r 0 =1.5 mm, and derive a set of new analytical equations to calculate the spatial distributions of the electrostatic field in the above charged-disk layout. Afterwards, we calculate the electric-field distributions of our electrostatic trap and the Stark potential for cold ND 3 molecules, and analyze the dependences of both the electric field and the Stark potential on the geometric parameters of our charged-disk scheme, and find an optimal condition to form a desirable trap with the same trap depth in the x , y , and z directions. Also, we propose a desirable scheme to realize an efficient loading of cold polar molecules in the weak-field-seeking states, and investigate the dependences of the loading efficiency on both the initial forward velocity of the incident molecular beam and the loading time by Monte Carlo simulations. Our study shows that the maximal loading efficiency of our trap scheme can reach about 95%, and the corresponding temperature of the trapped cold molecules is about 28.8 mK. Finally, we study the Stark-potential evaporative cooling for cold polar molecules in our trap by the Monte Carlo method, and find that our simulated evaporative cooling results are consistent with our developed analytical model based on trapping-potential evaporative cooling.We propose a novel optical-access opened electrostatic trap to study the Stark-potential evaporative cooling of polar molecules by using two charged disk electrodes with a central hole of radius r 0 =1.5 mm, and derive a set of new analytical equations to calculate the spatial distributions of the electrostatic field in the above charged-disk layout. Afterwards, we calculate the electric-field distributions of our electrostatic trap and the Stark potential for cold ND 3 molecules, and analyze the dependences of both the electric field and the Stark potential on the geometric parameters of our charged-disk scheme, and find an optimal condition to form a desirable trap with the same trap depth in the x , y , and z directions. Also, we propose a desirable scheme to realize an efficient loading of cold polar molecules in the weak-field-seeking states, and investigate the dependences of the loading efficiency on both the initial forward velocity of the incident molecular beam and the loading time by Monte Carlo simulations. Our study shows that the maximal loading efficiency of our trap scheme can reach about 95%, and the corresponding temperature of the trapped cold molecules is about 28.8 mK. Finally, we study the Stark-potential evaporative cooling for cold polar molecules in our trap by the Monte Carlo method, and find that our simulated evaporative cooling results are consistent with our developed analytical model based on trapping-potential evaporative cooling.

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Cold ion–polar-molecule reactions studied with a combined Stark-velocity-filter–ion-trap apparatus

K. Okada, T Suganuma, Takahiro Furukawa +3 more

We have developed a combined Stark-velocity-filter--ion-trap apparatus for the purpose of reaction-rate measurements between cold trapped ions and slow polar molecules under ultrahigh vacuum conditions. The prerequisite steps such as the characterization of velocity-selected polar molecules (PM), namely ND ${}_{3}$ , H ${}_{2}$ CO, and CH ${}_{3}$ CN, were performed using time-of-flight (TOF) measurements. We confirmed the generation of slow ND ${}_{3}$ , H ${}_{2}$ CO, and CH ${}_{3}$ CN molecules having thermal energies of a few Kelvin. Additionally, the number densities of the slow velocity-filtered polar molecules were determined to be in the range of $n={10}^{4}$ to 10 ${}^{6}$ cm${}^{\ensuremath{-}3}$ by calibrating the TOF signals. In a first experiment, the Stark velocity filter was connected to a cryogenic linear Paul trap and reaction-rate measurements between laser-cooled Ca ${}^{+}$ Coulomb crystals and velocity-selected polar molecules were carried out. The observed reaction rates are of the order of 10${}^{\ensuremath{-}5}$ s${}^{\ensuremath{-}1}$, which are much slower than typical reaction rates of molecular ion--polar-molecule reactions at low temperatures. The present results confirm that reaction-rate measurements between velocity-selected polar molecules and sympathetically cooled molecular ions cooled by a laser-cooled Ca ${}^{+}$ Coulomb crystal can be performed. Next we measured the reaction rates between sympathetically cooled nonfluorescent stored ion molecules namely N ${}_{2}$ H ${}^{+}$ ions and velocity-selected CH ${}_{3}$ CN molecules at the average reaction energy of about 3 K. The measured reaction rate of 2.0(2)$\ifmmode\times\else\texttimes\fi{} $10$ {}^{\ensuremath{-}3}$ s${}^{\ensuremath{-}1}$ is much faster than those of the Ca ${}^{+}$ +PM reactions. This is strong evidence that the velocity-selected polar molecules undergo reactive collisions. We also confirmed that the present reaction-rate constant of CH ${}_{3}$ CN+N ${}_{2}$ H ${}^{+}$ $\ensuremath{\rightarrow}$ CH ${}_{3}$ CNH ${}^{+}$ +N ${}_{2}$ is consistent with the estimated values from the room temperature results and the trajectory-scaling formula of Su et al. In the future, the present velocity-filter combined cryogenic trap apparatus will enable us to perform systematic measurements of cold ion--polar-molecule reactions, which are important problems from a fundamental viewpoint and also contribute to astrochemistry.We have developed a combined Stark-velocity-filter--ion-trap apparatus for the purpose of reaction-rate measurements between cold trapped ions and slow polar molecules under ultrahigh vacuum conditions. The prerequisite steps such as the characterization of velocity-selected polar molecules (PM), namely ND${}_{3}$, H${}_{2}$CO, and CH${}_{3}$CN, were performed using time-of-flight (TOF) measurements. We confirmed the generation of slow ND${}_{3}$, H${}_{2}$CO, and CH${}_{3}$CN molecules having thermal energies of a few Kelvin. Additionally, the number densities of the slow velocity-filtered polar molecules were determined to be in the range of $n={10}^{4}$ to 10${}^{6}$ cm${}^{\ensuremath{-}3}$ by calibrating the TOF signals. In a first experiment, the Stark velocity filter was connected to a cryogenic linear Paul trap and reaction-rate measurements between laser-cooled Ca${}^{+}$ Coulomb crystals and velocity-selected polar molecules were carried out. The observed reaction rates are of the order of 10${}^{\ensuremath{-}5}$ s${}^{\ensuremath{-}1}$, which are much slower than typical reaction rates of molecular ion--polar-molecule reactions at low temperatures. The present results confirm that reaction-rate measurements between velocity-selected polar molecules and sympathetically cooled molecular ions cooled by a laser-cooled Ca${}^{+}$ Coulomb crystal can be performed. Next we measured the reaction rates between sympathetically cooled nonfluorescent stored ion molecules namely N${}_{2}$H${}^{+}$ ions and velocity-selected CH${}_{3}$CN molecules at the average reaction energy of about 3 K. The measured reaction rate of 2.0(2)$\ifmmode\times\else\texttimes\fi{}$10${}^{\ensuremath{-}3}$ s${}^{\ensuremath{-}1}$ is much faster than those of the Ca${}^{+}$+PM reactions. This is strong evidence that the velocity-selected polar molecules undergo reactive collisions. We also confirmed that the present reaction-rate constant of CH${}_{3}$CN+N${}_{2}$H${}^{+}$ $\ensuremath{\rightarrow}$ CH${}_{3}$CNH${}^{+}$+N${}_{2}$ is consistent with the estimated values from the room temperature results and the trajectory-scaling formula of Su et al. In the future, the present velocity-filter combined cryogenic trap apparatus will enable us to perform systematic measurements of cold ion--polar-molecule reactions, which are important problems from a fundamental viewpoint and also contribute to astrochemistry.

Physical Review AApr 26, 201324 citations

A continuously operated electrostatic trap for polar molecules is demonstrated. The trap has a volume of

\ensuremath{\approx}0.6\text{ }\text{ }{\mathrm{cm}}^{3}

and holds molecules with a positive Stark shift. With deuterated ammonia from a quadrupole velocity filter, a trap density of

\ensuremath{\approx}{10}^{8}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}

is achieved with an average lifetime of 130 ms and a motional temperature of

\ensuremath{\approx}300\text{ }\text{ }\mathrm{mK}

. The trap offers good starting conditions for high-precision measurements, and can be used as a first stage in cooling schemes for molecules and as a ``reaction vessel'' in cold chemistry.

({\mathrm{H}}_{2}\mathrm{CO})

and deuterated ammonia

({\mathrm{ND}}_{3}).

With

{\mathrm{H}}_{2}\mathrm{CO}

a continuous flux is measured of $\ensuremath{\approx}{10}^{9}/\mathrm{s}$ and a longitudinal temperature of a few kelvin. The data are compared with the result of a Monte Carlo simulation.

{}_{3}

, H

{}_{2}

CO, and CH

{}_{3}

CN, were performed using time-of-flight (TOF) measurements. We confirmed the generation of slow ND

{}_{3}

, H

{}_{2}

CO, and CH

{}_{3}

CN molecules having thermal energies of a few Kelvin. Additionally, the number densities of the slow velocity-filtered polar molecules were determined to be in the range of

n={10}^{4}

to 10

{}^{6}

cm${}^{\ensuremath{-}3}$ by calibrating the TOF signals. In a first experiment, the Stark velocity filter was connected to a cryogenic linear Paul trap and reaction-rate measurements between laser-cooled Ca

{}^{+}

Coulomb crystals and velocity-selected polar molecules were carried out. The observed reaction rates are of the order of 10${}^{\ensuremath{-}5}$ s${}^{\ensuremath{-}1}$, which are much slower than typical reaction rates of molecular ion--polar-molecule reactions at low temperatures. The present results confirm that reaction-rate measurements between velocity-selected polar molecules and sympathetically cooled molecular ions cooled by a laser-cooled Ca

{}^{+}

Coulomb crystal can be performed. Next we measured the reaction rates between sympathetically cooled nonfluorescent stored ion molecules namely N

{}_{2}

{}^{+}

ions and velocity-selected CH

{}_{3}

CN molecules at the average reaction energy of about 3 K. The measured reaction rate of 2.0(2)$\ifmmode\times\else\texttimes\fi{}

10

{}^{\ensuremath{-}3}$ s${}^{\ensuremath{-}1}$ is much faster than those of the Ca

{}^{+}

+PM reactions. This is strong evidence that the velocity-selected polar molecules undergo reactive collisions. We also confirmed that the present reaction-rate constant of CH

{}_{3}

CN+N

{}_{2}

{}^{+}

$\ensuremath{\rightarrow}$ CH

{}_{3}

CNH

{}^{+}

{}_{2}

is consistent with the estimated values from the room temperature results and the trajectory-scaling formula of Su et al. In the future, the present velocity-filter combined cryogenic trap apparatus will enable us to perform systematic measurements of cold ion--polar-molecule reactions, which are important problems from a fundamental viewpoint and also contribute to astrochemistry.