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Title:Pulsed plasma microjets: a new tool for the investigation of plasma kinetics and molecular spectroscopy
Author(s):Houlahan, Thomas
Director of Research:Eden, James G.
Doctoral Committee Chair(s):Eden, James G.
Doctoral Committee Member(s):Carney, Paul S.; Cunningham, Brian T.; Gruebele, Martin; McCall, Benjamin J.
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(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).
Issue Date:2015-01-21
Rights Information:Copyright 2014 Thomas J. Houlahan, Jr.
Date Available in IDEALS:2015-01-21
Date Deposited:2014-12

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