Beam Action Spectroscopy via Inelastic Scattering BASIS Technique Bobby H. Layne and Liam M. Duffy Department of Chemistry & Biochemistry, the University of North Carolina at Greensboro, Greensboro, North Carolina 27402 Hans A Bechtel, Adam H. Steeves and Robert W. Field Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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Beam Action Spectroscopy via Inelastic Scattering BASIS Technique Bobby H. Layne and Liam M. Duffy Department of Chemistry & Biochemistry, the University.
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Beam Action Spectroscopy via Inelastic Scattering
BASIS Technique
Bobby H. Layne and Liam M. DuffyDepartment of Chemistry & Biochemistry, the University of North
Carolina at Greensboro, Greensboro, North Carolina 27402
Hans A Bechtel, Adam H. Steeves and Robert W. FieldDepartment of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
J. Phys. Chem. A (online)
Current Research
Using mm-Waves to probe:
• Photodissociation of atmospheric molecules:– characterizing quantum state distribution of products
– hyper-rovibronic detail
• Crossed molecular beams: reactive and inelastic scattering dynamics
Current Photodissociation Study
Chlorine Dioxide
h
Chlorine MonoxideOxygen
ClCl
OOO
O
Parent Molecule Products
OClO is an reservoir molecule for Cl radicals in the atmosphere
OClO Mode Specific UV Spectrum
0.0E+00
2.0E-18
4.0E-18
6.0E-18
8.0E-18
1.0E-17
1.2E-17
1.4E-17
1.6E-17
280 300 320 340 360 380 400 420 440
Wavelength (nm)
Ab
sorp
tion
Cro
ss S
ecti
on (
cm2 )
204 K
(14,
0,0)
(16,
0,0)
(18,
0,0)
(15,
0,0)
(17,
0,0)
(6,0
,0)
(5,0
,2)
(6,1
,0)
(1, 2, 3 )sym, bend, asym
(5,1
,2)
This Study
A. Wahner, G. S. Tyndall, and A. R. Ravishankara, J. Phys. Chem. 91, 2734 (1987).
• Gain: – energy deposited in beam is large– e.g. 6x over traditional hole burning (f )– analogous to optothermal technique (but simpler)– may extend the sensitivity of direct-IR absorption
• General Method:– should work for any rotationally resolved
molecular beam spectroscopic technique
Best BASIS Conditions
• Cold rotational distribution
• High density region:– reporting molecule needs to stay in the beam– near nozzle for IR BASIS– down stream possible for slit jet photodissociation
• Reporting molecule chosen:– largest rotational line intensity – does not photodissociate– large RT collision cross section?
Possible BASIS Experiments• UV, Vis, IR – BASIS• Dark states• Surface BASIS:
– scattering off of optically excited SAMs
Side Implications• Slit-jet densities are so large that fragments are
entrained even 10 cm downstream• Pump-probe time delay important, particularly in CW
experiments– Lifetime broadening may be collisional broadening.
(e.g. OClO near Frank-Condon max)
Acknowledgements
UNCG Undergraduate:Bobby H. Layne
Hans A Bechtel, Adam H. Steeves and Robert W. Field
H.A.B. acknowledges the Donors of the AmericanChemical Society Petroleum Research Fund for support, andA.H.S. acknowledges the Army Research Office for a NationalDefense Science and Engineering Graduate Fellowship. The
work at MIT was supported by the Office of Basic EnergySciences of the U.S. Department of Energy
Helpful conversations & BASIS acronym:Prof. Robert M. Whitnell