Pulsed plasma microjets: a new tool for the investigation of plasma kinetics and molecular spectroscopy

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).

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Houlahan, Thomas

Contributors dc:contributor

• Eden, James G.
• Carney, Paul S.
• Cunningham, Brian T.
• Gruebele, Martin
• McCall, Benjamin J.

• supersonic cooling
• plasma jet
• short-lived molecular states

Statement dc:rights

• Copyright 2014 Thomas J. Houlahan, Jr.

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/72742

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/72742