{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/72742"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/72742","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Pulsed plasma microjets: a new tool for the investigation of plasma kinetics and molecular spectroscopy","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).","abstract_html":"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).","abstract_has_math":false,"creators":["Houlahan, Thomas"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Electrical & Computer Engr","degree_department":null,"school":null,"contributors":["Eden, James G.","Carney, Paul S.","Cunningham, Brian T.","Gruebele, Martin","McCall, Benjamin J."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2015,"date_issued":"2015-01-21T19:47:36Z","date_published":"2015-01-21T19:47:36Z","updated_at":"2026-07-22T22:26:07Z","subjects":["supersonic cooling","plasma jet","short-lived molecular states"],"languages":["en"],"rights":["Copyright 2014 Thomas J. 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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).","Item withdrawn by Laura Spradlin (lspradl2@illinois.edu) on 2014-08-07T21:52:47Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Houlahan_Thomas.pdf: 14547007 bytes, checksum: 8703d2837c86e52f240847d778dbca60 (MD5)","Made available in DSpace on 2015-01-21T19:47:36Z (GMT). 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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).","Item withdrawn by Laura Spradlin (lspradl2@illinois.edu) on 2014-08-07T21:52:47Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Houlahan_Thomas.pdf: 14547007 bytes, checksum: 8703d2837c86e52f240847d778dbca60 (MD5)","Made available in DSpace on 2015-01-21T19:47:36Z (GMT). No. of bitstreams: 1 Thomas_Houlahan.pdf: 14547007 bytes, checksum: 8703d2837c86e52f240847d778dbca60 (MD5)"],"dc:identifier":["http://hdl.handle.net/2142/72742"],"dc:language":["en"],"dc:rights":["Copyright 2014 Thomas J. 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