Difference between revisions of "Clustering"
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==Overview== | ==Overview== | ||
| − | [[ | + | [[20140128_cell_geometry_current_run_OPO_shaping.png|thumb|500px|Schematic of experimental setup. ]] |
Cryogenic helium buffer gases have cooled a diversity of molecules to temperatures ~1 K. Driven by collisional physics studies, as well as mixture and chiral analysis, we are now cooling larger (often biological) molecules. A detailed understanding of helium-molecule sticking is currently unknown, as is any (related) possible molecular size limit of buffer gas cooling. We explore He-molecule collisions at energies well below their binding energy, where the pair would form a dimer (or a larger cluster) under equilibrium conditions. Molecules from an oven source (300-500 K) flow into a cold (5 K) cell, where they undergo a few hundred collisions with He that is at a density of ~10^14 cm^-3. Using laser fluorescence, we observe translational and internal cooling of benzonitrile, benzonitrile dimers, trans-stilbene and the significantly larger molecule Nile Red. Narrow, unperturbed spectral lines in trans-stilbene indicate the gas-phase monomer. Our spectra of Nile Red -- the first ever taken in the gas-phase -- also indicates cold monomer. In Nile Red, we also see broad spectral features that are possibly consistent with the creation of a molecule-molecule dimer population. We see no evidence of high He-molecule dimer formation rates (in either species) and conclude that for these molecules (as well as smaller molecules cooled in earlier work [1]) the lifetime of possible helium-molecule dimers is below ~1 microsecond. | Cryogenic helium buffer gases have cooled a diversity of molecules to temperatures ~1 K. Driven by collisional physics studies, as well as mixture and chiral analysis, we are now cooling larger (often biological) molecules. A detailed understanding of helium-molecule sticking is currently unknown, as is any (related) possible molecular size limit of buffer gas cooling. We explore He-molecule collisions at energies well below their binding energy, where the pair would form a dimer (or a larger cluster) under equilibrium conditions. Molecules from an oven source (300-500 K) flow into a cold (5 K) cell, where they undergo a few hundred collisions with He that is at a density of ~10^14 cm^-3. Using laser fluorescence, we observe translational and internal cooling of benzonitrile, benzonitrile dimers, trans-stilbene and the significantly larger molecule Nile Red. Narrow, unperturbed spectral lines in trans-stilbene indicate the gas-phase monomer. Our spectra of Nile Red -- the first ever taken in the gas-phase -- also indicates cold monomer. In Nile Red, we also see broad spectral features that are possibly consistent with the creation of a molecule-molecule dimer population. We see no evidence of high He-molecule dimer formation rates (in either species) and conclude that for these molecules (as well as smaller molecules cooled in earlier work [1]) the lifetime of possible helium-molecule dimers is below ~1 microsecond. | ||
* [1] D. Patterson and J. Doyle, Cooling molecules in a cell for FTMW spectroscopy," Molecular Physics, vol. 110, pp. 1757{1766, 2012. | * [1] D. Patterson and J. Doyle, Cooling molecules in a cell for FTMW spectroscopy," Molecular Physics, vol. 110, pp. 1757{1766, 2012. | ||
Revision as of 13:32, 12 March 2014
People
Julia Piskorski
David Patterson
Overview
thumb|500px|Schematic of experimental setup. Cryogenic helium buffer gases have cooled a diversity of molecules to temperatures ~1 K. Driven by collisional physics studies, as well as mixture and chiral analysis, we are now cooling larger (often biological) molecules. A detailed understanding of helium-molecule sticking is currently unknown, as is any (related) possible molecular size limit of buffer gas cooling. We explore He-molecule collisions at energies well below their binding energy, where the pair would form a dimer (or a larger cluster) under equilibrium conditions. Molecules from an oven source (300-500 K) flow into a cold (5 K) cell, where they undergo a few hundred collisions with He that is at a density of ~10^14 cm^-3. Using laser fluorescence, we observe translational and internal cooling of benzonitrile, benzonitrile dimers, trans-stilbene and the significantly larger molecule Nile Red. Narrow, unperturbed spectral lines in trans-stilbene indicate the gas-phase monomer. Our spectra of Nile Red -- the first ever taken in the gas-phase -- also indicates cold monomer. In Nile Red, we also see broad spectral features that are possibly consistent with the creation of a molecule-molecule dimer population. We see no evidence of high He-molecule dimer formation rates (in either species) and conclude that for these molecules (as well as smaller molecules cooled in earlier work [1]) the lifetime of possible helium-molecule dimers is below ~1 microsecond.
- [1] D. Patterson and J. Doyle, Cooling molecules in a cell for FTMW spectroscopy," Molecular Physics, vol. 110, pp. 1757{1766, 2012.
