Hot Cold Molecules: Collisions at Astrophysical Temperatures

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Hot Cold Molecules Collisions at Astrophysical
Temperatures Frank C. De Lucia Ohio State
University
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Atom Envy, Molecule Envy the Grass is Greener
on the Other Side of the Fence Atom
Envy Science Rotational and Vibrational
Partition Function Dilution of Oscillator
Strength Complexity of Open Collisional
Channels hard theory classical
results Preclusion of many cooling
techniques Technology Photon gtgt kT Molecule
Envy?
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THE ENERGETICS
Atoms and Molecules E (electronic) 50000 cm-1 E
(vibrational) 1000 cm-1 E (rotational) 1
cm-1 E (fine structure) 0.01 cm-1 Radiation UV/
Vis gt 3000 cm-1 IR 300 - 3000 cm-1 FIR 30 - 300
cm-1 MW 1 - 30 cm-1 RF lt 1 cm-1
Temperature kT (300 K) 200 cm-1 kT (1.5 K) 1
cm-1 kT (0.001 K) 0.0007 cm-1 Fields qE
(electron) gtgt 100000 cm-1 mE (1 D) 1 cm-1 mB
(electronic) 1 cm-1 mB (nuclear) 0.001 cm-1
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Overview Why have we been interested in hot
cold molecules? What are the techniques we have
developed? What kinds of science have we done?
What is the physics in the regime where kT hnr
Vwell? What kinds of results have been
obtained? A fundamental experimental -
theoretical gap?
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Why Have We Been Interested? To explore new
experimental regime A regime in which exact
calculations are possible A regime where the
results are quantal and interesting Collisions in
the Astrophysical Regime
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COLLISION COOLING AN APPROACH TO GAS PHASE
STUDIES AT VERY LOW TEMPERATURES
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Typical Spectra - HCN
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Other Systems
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INELASTIC CROSS SECTIONS
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QUANTUM COLLISIONS
300 K 1 K ________________________
__________
Correspondence Principle The predictions of the
quantum theory for the behavior of any physical
system must correspond to the prediction of
classical physics in the limit in which the
quantum numbers specifying the state of the
system become very large.
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CROSS SECTIONS FOR CO-He COLLISIONS
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Calculated Pressure Broadening Cross Sections
for HCN - He
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AN ATOM-MOLECULE COLLISION
Before During
After
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MOLECULAR ENGINEERING - TEST
Rotational Spacing Decreased by 5 (dashed)
Well Depth Increased by 2 (dashed)
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H2S - He COLLISION CROSS SECTIONS
Pressure broadening (open squares) and inelastic
(solid circles) cross sections for the 110 - 101
transition
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HCN 1?0 Elastic Cross Section
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CO-He CROSS SECTIONS
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Doppler Width Are the molecules cooled to the
same temperature as the walls of the cell?
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What Underlies the Difference between Experiment
and Theory? The Theory Quantum Scattering
Calculations Impact Approximation
Intermolecular Potential ab initio from
Quantum Chemistry Inversion of bound
state energy levels The Experiment The
Pressure - Transpiration The Frequency
Measurements The Temperature Measurements
THE JOURNAL OF CHEMICAL PHYSICS 105, 4005
(1996) Linewidths and shift of very low
temperature CO in He A challenge for theory or
experiment Mark Thachuk, Claudio
E. Chuaqui, and Robert J. Le Roy
Department of Chemistry, The University of
Waterloo
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A Hint? - Contributions To sPB
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COLLISIONAL COOLING APPARATUS
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SCALING PARAMETERS
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POTENTIAL WELL AND COLLISION CROSS SECTIONS
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EFFECT OF INCREASED WELL DEPTH
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H2S - He COLLISION CROSS SECTIONS
110 - 101 Broadening and Shift
220 - 211 Broadening and Shift
110 - 101 Broadening and Inelastic
THEORY counterpoise corrected (solid line)
counterpoise uncorrected (dashed line)