Condensation limited cooling in supersonic expansions

Hillenkamp, Matthias; Keinan, Sharon; Even, U.

doi:10.1063/1.1568331

Cited by 122 publications

(111 citation statements)

References 24 publications

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“…A gas mixture of ∼10 mbar carbonyl sulfide (OCS) and 10 bar of Ne is expanded supersonically into vacuum through an Even-Lavie valve [34,35], forming a pulsed molecular beam. The molecular beam is skimmed twice before entering a 15-cm-long electrostatic deflector that spatially disperses the molecular beam in the vertical direction according to the quantum states populated [29,30].…”

Section: Experimental Methodsmentioning

confidence: 99%

Ionization of oriented carbonyl sulfide molecules by intense circularly polarized laser pulses

et al. 2011

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We present combined experimental and theoretical results on strong-field ionization of oriented carbonyl sulfide molecules by circularly polarized laser pulses. The obtained molecular frame photoelectron angular distributions show pronounced asymmetries perpendicular to the direction of the molecular electric dipole moment. These findings are explained by a tunneling model invoking the laser-induced Stark shifts associated with the dipoles and polarizabilities of the molecule and its unrelaxed cation. The focus of the present article is to understand the strong-field ionization of one-dimensionally-oriented polar molecules, in particular asymmetries in the emission direction of the photoelectrons. In the following article [Phys. Rev. A 83, 023406 (2011)] the focus is to understand strong-field ionization from three-dimensionally-oriented asymmetric top molecules, in particular the suppression of electron emission in nodal planes of molecular orbitals.

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Section: Experimental Methodsmentioning

confidence: 99%

Ionization of oriented carbonyl sulfide molecules by intense circularly polarized laser pulses

et al. 2011

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“…turbomolecular pump, followed by the deflector and the target chamber which are both pumped by 500-l/s turbomolecular pumps. The molecular beam is formed by expanding a mixture of carrier gas (typically 90 bar of helium) and the molecular gas (∼5 mbar of benzonitrile) into the source chamber through a high-pressure Even-Lavie valve [26,27] heated to 40 • C. We estimate the rotational temperature of the molecular gas by (i) comparing experimentally observed degrees of alignment with theoretical calculations for a temperature averaged sample of molecules [28] or (ii) by comparing measured vertical molecular beam profiles of electrostatically deflected molecules with simulations [29]. We find that the typical rotational temperature is ∼1 K. The experiments are performed at 20 Hz limited by the repetition rate of the alignment laser.…”

Section: A Molecular Beam Apparatusmentioning

confidence: 99%

Ionization of one- and three-dimensionally-oriented asymmetric-top molecules by intense circularly polarized femtosecond laser pulses

et al. 2011

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We present a combined experimental and theoretical study on strong-field ionization of a three-dimensionallyoriented asymmetric top molecule, benzonitrile (C 7 H 5 N), by circularly polarized, nonresonant femtosecond laser pulses. Prior to the interaction with the strong field, the molecules are quantum-state selected using a deflector and three-dimensionally (3D) aligned and oriented adiabatically using an elliptically polarized laser pulse in combination with a static electric field. A characteristic splitting in the molecular frame photoelectron momentum distribution reveals the position of the nodal planes of the molecular orbitals from which ionization occurs. The experimental results are supported by a theoretical tunneling model that includes and quantifies the splitting in the momentum distribution. The focus of the present article is to understand strong-field ionization from 3D-oriented asymmetric top molecules, in particular the suppression of electron emission in nodal planes of molecular orbitals. In the preceding article [Dimitrovski et al., Phys. Rev. A 83, 023405 (2011)] the focus is to understand the strong-field ionization of one-dimensionally-oriented polar molecules, in particular asymmetries in the emission direction of the photoelectrons.

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“…In the case of noble gases it is well known that He does not form clusters in typical supersonic jets [191,195]. This is because He dimers are unstable and thus trimers are the smallest available cluster size, which only form at very low temperatures on the milliKelvin level.…”

Section: Cooling Mechanismmentioning

confidence: 99%

“…As was discussed in section 4.4.4, seeding of the molecule in an atomic carrier gas may lead to enhanced rotational cooling of the seed during a supersonic expansion. Yet, the cooling efficiency sensitively depends on the atomic carrier species [195] and the properties of the gas jet like nozzle dimensions, molecular beam skimming [197,224] and backing pressure [195,198]. Typically however, the geometrical characteristics of the gas jet such as nozzle and skimmer properties and distances cannot be varied.…”

Section: Impact Of the Rotational Temperaturementioning

confidence: 99%

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Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

Oppermann

2014

Springer Theses

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In this thesis, the role of the molecular structure in strong field induced processes in CO 2 is resolved by the use of optimised impulsive molecular alignment. Two processes were investigated: recollision induced ionisation and the dissociation of the molecular ion CO + 2 . Both processes are driven by the initial tunneling ionisation of CO 2 . Through the use of molecular alignment, the orbital symmetries of the involved molecular ionic states were resolved, revealing the internal molecular dynamics in the form of ionisation and excitation pathways.A novel data analysis procedure was developed to extract the alignment distribution and rotational temperature of the impulsively aligned molecular ensemble. This facilitated the optimisation of molecular alignment in mixed gas samples and was demonstrated for N 2 , O 2 and CO 2 seeded in Ar.The recollision induced or nonsequential double ionisation (NSDI) of CO 2 was then studied in the molecular frame. The process was fully characterised by measuring the shape of the recolliding electron wavepacket and the angularly resolved inelastic electronion recollision cross section. The results reveal the contribution from both the ionic ground and first excited state of CO + 2 to the NSDI mechanism. This study was extended to the strong field induced dissociation of impulsively aligned CO + 2 . It was found that dissociation is driven by a parallel dipole transition from the second excited ionic state B to the predissociating state C, whilst recollision excitation was shown to not play a role. The strong field induced coupling of the ionic states B and C could thus be controlled by the laser polarisation.The results obtained in this thesis further the understanding of population dynamics of cation states in strong field processes. This is of special interest for extending molecular strong field physics to the study of electronic degrees of freedom and their coupling to the nuclear motion. had hoped for in a research degree and I cannot thank Jon enough for making it such an enriching experience, both professionally and personally.

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Condensation limited cooling in supersonic expansions

Cited by 122 publications

References 24 publications

Ionization of oriented carbonyl sulfide molecules by intense circularly polarized laser pulses

Ionization of oriented carbonyl sulfide molecules by intense circularly polarized laser pulses

Ionization of one- and three-dimensionally-oriented asymmetric-top molecules by intense circularly polarized femtosecond laser pulses

Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

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