1. Hot Cold Molecules: Collisions at Astrophysical Temperatures
Frank C. De Lucia
Ohio State University

2. 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 >> kT
Molecule Envy?

3. THE ENERGETICS Atoms and Molecules Temperature Fields Radiation
E (electronic) ~ cm-1
E (vibrational) ~ 1000 cm-1
E (rotational) ~ 1 cm-1
E (fine structure) ~ 0.01 cm-1
Radiation
UV/Vis > 3000 cm-1
IR cm-1
FIR cm-1
MW cm-1
RF < 1 cm-1
Temperature
kT (300 K) = 200 cm-1
kT (1.5 K) = 1 cm-1
kT (0.001 K) = cm-1
Fields
qE (electron) >> cm-1
mE (1 D) ~ 1 cm-1
mB (electronic) ~ 1 cm-1
mB (nuclear) ~ cm-1

4. 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?

5. 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

6. COLLISION COOLING: AN APPROACH TO GAS PHASE STUDIES AT VERY LOW TEMPERATURES

7. Typical Spectra - HCN

8. Other Systems

9. INELASTIC CROSS SECTIONS

10. Correspondence Principle
QUANTUM COLLISIONS
300 K 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.

11. CROSS SECTIONS FOR CO-He COLLISIONS

12. Calculated Pressure Broadening Cross Sections for HCN - He

13. AN ATOM-MOLECULE COLLISION
Before During After

14. MOLECULAR ENGINEERING - TEST
Rotational Spacing Decreased by 5% (dashed)
Well Depth Increased by 2% (dashed)

15. H2S - He COLLISION CROSS SECTIONS
Pressure broadening (open squares) and inelastic (solid circles) cross sections for the transition

16. 10 Elastic Cross Section
HCN
10 Elastic Cross Section

17. CO-He CROSS SECTIONS

18. Doppler Width
Are the molecules cooled to the same temperature as the walls of the cell?

19. 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

20. A Hint? - Contributions To sPB

21. COLLISIONAL COOLING APPARATUS

22. SCALING PARAMETERS CO H S CH Cl He 18.8 57.8 61.9 34.7 106.5 114.1 Rb2 S CH 3 Cl He
18.8
57.8
61.9
34.7
106.5
114.1 Rb
10.74
450

23. POTENTIAL WELL AND COLLISION CROSS SECTIONS

24. EFFECT OF INCREASED WELL DEPTH

25. H2S - He COLLISION CROSS SECTIONS
Broadening and Shift
Broadening and Shift
Broadening and Inelastic
THEORY
counterpoise corrected (solid line) counterpoise uncorrected (dashed line)