Intense pulsed helium droplet beams

Slipchenko, Mikhail N.; Kuma, Susumu; Momose, Takamasa; Vilesov, Andrey F.

doi:10.1063/1.1505661

Cited by 69 publications

(82 citation statements)

References 44 publications

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“…This flux, and thus sensitivity, can be greatly enhanced by utilizing one of the recently developed pulsed helium droplet sources. 29,30 However, it should be realized that the ultimate sensitivity when using these pulsed sources will be determined by the background signal caused by the direct non-resonant ionization of molecules in helium droplets by the femtosecond laser pulse. Besides being more sensitive, the new technique has an additional advantage, i.e.…”

Section: Discussionmentioning

confidence: 99%

A new sensitive detection scheme for helium nanodroplet isolation spectroscopy: application to benzene

Loginov

Braun

Drabbels

2008

Phys. Chem. Chem. Phys.

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A new method is presented for recording excitation spectra of molecules embedded in helium nanodroplets. The method relies on the complete evaporation of the droplets following excitation of a dissolved molecule and the subsequent detection of the remaining unsolvated molecule by mass spectrometry. The technique has been successfully applied to record the S 1 1 B 2u ' S 0 1 A 1g transition in benzene. The transition frequencies determined by this new method, beam depletion spectroscopy and REMPI spectroscopy have been found to differ slightly from each other. It is argued that these differences in transition frequency are related to the different droplet sizes probed by the spectroscopic techniques.

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Section: Discussionmentioning

confidence: 99%

A new sensitive detection scheme for helium nanodroplet isolation spectroscopy: application to benzene

Loginov

Braun

Drabbels

2008

Phys. Chem. Chem. Phys.

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“…High purity helium (99.9999%) was employed at a typical stagnation pressure of 20 bar and a nozzle temperature of 11 K. Under similar experimental conditions Vilesov and coworkers determined an average droplet size of 5 Â 10 4 helium atoms. 18 We have independently determined the droplet sizes in our experiments using a procedure that has been described in detail elsewhere and parallels that used by many other research groups. 19 Briefly, the probability that a droplet acquires one or more dopant molecules is governed by Poisson statistics.…”

Section: Methodsmentioning

confidence: 99%

Soft or hard ionization of molecules in helium nanodroplets? An electron impact investigation of alcohols and ethers

Yang

Brereton

Wheeler

et al. 2005

Phys. Chem. Chem. Phys.

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Electron impact (70 eV) mass spectra of a series of C 1 -C 6 alcohols encased in large superfluid liquid helium nanodroplets (B60 000 helium atoms) have been recorded. The presence of helium alters the fragmentation patterns when compared with the gas phase, with some ion product channels being more strongly affected than others, most notably cleavage of the C a -H bond in the parent ion to form the corresponding oxonium ion. Parent ion intensities are also enhanced by the helium, but only for the two cyclic alcohols studied, cyclopentanol and cyclohexanol, is this effect large enough to transform the parent ion from a minor product (in the gas phase) into the most abundant ion in the helium droplet experiments. To demonstrate that these findings are not unique to alcohols, we have also investigated several ethers. The results obtained for both alcohols and ethers are difficult to explain solely by rapid cooling of the excited parent ions by the surrounding superfluid helium, although this undoubtedly takes place. A second factor also seems to be involved, a cage effect which favors hydrogen atom loss over other fragmentation channels. The set of molecules explored in this work suggest that electron impact ionization of doped helium nanodroplets does not provide a sufficiently large softening effect to be useful in analytical mass spectrometry.

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“…With a straight channel of 0.5 mm diameter drilled through the faceplate the result was little ability to control the droplet size and a restriction to large droplets ͑average sizes Ͼ5 ϫ 10 4 helium atoms͒. We next turned to the conical nozzle design reported by Slipchenko et al, 2 where the converging and diverging cones meet at a simple knife-edge junction. In agreement with Slipchenko and co-workers, we again found that the ability to vary the droplet size in a systematic way was limited.…”

Section: Methodsmentioning

confidence: 99%

“…The valve is cooled by contact with a closed-cycle cryostat which is capable of achieving temperatures as low as 4 K. The operating mechanism of the valve uses a retractable poppet to open and close the aperture. Following Slipchenko et al, 2 we employ a poppet made from Kel-F, a material which is able to withstand a͒ Author to whom correspondence should be addressed; electronic mail: andrew.ellis@le.ac.uk repetitive use at low temperatures without fracture. A leaktight seal between the walls of the valve body and the faceplate is achieved using an indium gasket.…”

Section: Methodsmentioning

confidence: 99%

“…In this seminal work Slipchenko et al succeeded in producing repetitive pulses of helium droplets by modifying a commercially available pulsed valve such that it could operate at cryogenic temperatures. 2 A comparison of the performance of the pulsed source with conventional continuous supersonic expansion sources revealed a much higher helium droplet flux with the former. In addition, a pulsed source allows the use of smaller vacuum pumps, reduces the consumption of expensive high-purity helium, and is better suited to experiments in which the droplets are probed by pulsed lasers.…”

Section: Introductionmentioning

confidence: 99%

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Controlled growth of helium nanodroplets from a pulsed source

Yang

Brereton

Ellis

2005

Review of Scientific Instruments

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Factors affecting the size of liquid-helium droplets produced by a pulsed nozzle are described. The shape of the nozzle orifice is found to be important in allowing control of the size of the droplets. With an appropriate choice of nozzle geometry, the average droplet size is shown to be continuously variable over nearly two orders of magnitude by adjustment of the helium gas stagnation pressure and/or temperature. A scaling law similar to, but not identical with, that found for helium droplets produced by continuous supersonic expansion sources is found for the pulsed source. The pulsed nozzle described in this article has been used to make helium droplets ranging in size from a few thousand atoms up to nearly 10 5 helium atoms.

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Intense pulsed helium droplet beams

Cited by 69 publications

References 44 publications

A new sensitive detection scheme for helium nanodroplet isolation spectroscopy: application to benzene

A new sensitive detection scheme for helium nanodroplet isolation spectroscopy: application to benzene

Soft or hard ionization of molecules in helium nanodroplets? An electron impact investigation of alcohols and ethers

Controlled growth of helium nanodroplets from a pulsed source

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