Pulsed plasma microjets: a new tool for the investigation of plasma kinetics and molecular spectroscopy
Houlahan, Thomas
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Thomas_Houlahan.pdf
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https://hdl.handle.net/2142/72742
Description
Title
Pulsed plasma microjets: a new tool for the investigation of plasma kinetics and molecular spectroscopy
Author(s)
Houlahan, Thomas
Issue Date
2015-01-21
Director of Research (if dissertation) or Advisor (if thesis)
Eden, James G.
Doctoral Committee Chair(s)
Eden, James G.
Committee Member(s)
Carney, Paul S.
Cunningham, Brian T.
Gruebele, Martin
McCall, Benjamin J.
Department of Study
Electrical & Computer Eng
Discipline
Electrical & Computer Engr
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Date of Ingest
2015-01-21T19:47:36Z
Keyword(s)
supersonic cooling
plasma jet
short-lived molecular states
Abstract
We report on the development of a new laboratory tool which is suitable both for generating and quickly cooling short-lived molecules, and also for studying the kinetics and dynamics that take place at the rotational level during the expansion process. By integrating a microplasma device with a supersonic nozzle, temperatures as low as 50 K were achieved for molecules having lifetimes shorter than 40 ns and excitation (internal) energies ≳ 11 eV. Additionally, final temperatures ranging from 90 K to 900 K for a set of nested electronic states were observed in the He2 excimer, and a highly non-equilibrium rotational distribution was recorded for the lowest of these nested states. This rotational distribution was analyzed with a kinetic mode and shown to be due primarily to collisional excitation transfer and rotational relaxation. Since collisions are the means by which the supersonic expansion process cools atoms/molecules, this result perhaps demonstrates a fundamental restriction on which molecular states can and cannot be effectively cooled in a supersonic expansion. The rate constant for rotational relaxation within the He2(d3Σu+) state was determined to be (9.4 ± 0.1) × 10-13 cm3s-1, while the rate constant for collisional excitation transfer between rotational levels of the He2(e3Πg) and He2(d3Σu+) states was found to scale as (9.8 ± 5.9 × 10-14 cm3s-1)exp(-(6.4 × 10-3)/ ΔE*B).
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Thomas_Houlahan.pdf
