Multi-photon UV photolysis of gaseous polycyclic aromatic hydrocarbons: Extinction spectra and dynamics

dc.contributor.authorWalsh, Anton J.
dc.contributor.authorRuth, Albert A.
dc.contributor.authorGash, Edward W.
dc.contributor.authorMansfield, Michael W. D.
dc.contributor.funderEnterprise Irelanden
dc.contributor.funderHigher Education Authorityen
dc.contributor.funderScience Foundation Irelanden
dc.description.abstractThe extinction spectra of static naphthalene and static biphenylene vapor, each buffered with a noble gas at room temperature, were measured as a function of time in the region between 390 and 850 nm after UV multi-photon laser photolysis at 308 nm. Employing incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS), the spectra were found to be unstructured with a general lack of isolated features suggesting that the extinction was not solely based on absorption but was in fact dominated by scattering from particles formed in the photolysis of the respective polycyclic aromatic hydrocarbon. Following UV multi-photon photolysis, the extinction dynamics of the static (unstirred) closed gas-phase system exhibits extraordinary quasi-periodic and complex oscillations with periods ranging from seconds to many minutes, persisting for up to several hours. Depending on buffer gas type and pressure, several types of dynamical responses could be generated (classified as types I, II, and III). They were studied as a function of temperature and chamber volume for different experimental conditions and possible explanations for the oscillations are discussed. A conclusive model for the observed phenomena has not been established. However, a number of key hypotheses have made based on the measurements in this publication: (a) Following the multi-photon UV photolysis of naphthalene (or biphenylene), particles are formed on a timescale not observable using IBBCEAS. (b) The observed temporal behavior cannot be described on basis of a chemical reaction scheme alone. (c) The pressure dependence of the system's responses is due to transport phenomena of particles in the chamber. (d) The size distribution and the refractive indices of particles are time dependent and evolve on a timescale of minutes to hours. The rate of particle coagulation, involving coalescent growth and particle agglomeration, affects the observed oscillations. (e) The walls of the chamber act as a sink. The wall conditions (which could not be quantitatively characterized) have a profound influence on the dynamics of the system and on its slow return to an equilibrium state.en
dc.description.sponsorshipEnterprise Ireland (Basic Research Grant Scheme contract: SC/2003/96)); Higher Education Authority (HEA–PRTLI3 scheme)en
dc.description.statusPeer revieweden
dc.description.versionPublished Versionen
dc.identifier.citationWalsh, A. J., Ruth, A. A., Gash, E. W. and Mansfield, M. W. D. (2013) 'Multi-photon UV photolysis of gaseous polycyclic aromatic hydrocarbons: Extinction spectra and dynamics', The Journal of Chemical Physics, 139(5), 054304 (15 pp). doi: 10.1063/1.4816003en
dc.identifier.journaltitleJournal of Chemical Physicsen
dc.publisherAIP Publishingen
dc.relation.projectinfo:eu-repo/grantAgreement/SFI/SFI Research Frontiers Programme (RFP)/11/RFP.1/PHY/3233/IE/Anti-Stokes fluorescence of organic dyes: potential new materials for laser cooling in solids/en
dc.rights© 2013, AIP Publishing LLC. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in The Journal of Chemical Physics and may be found at
dc.subjectOrganic compoundsen
dc.subjectMultiphoton spectraen
dc.subjectRefractive indexen
dc.subjectExcited statesen
dc.subjectChemical equilibriumen
dc.subjectMolecule-photon collisionsen
dc.subjectExtinction coefficientsen
dc.titleMulti-photon UV photolysis of gaseous polycyclic aromatic hydrocarbons: Extinction spectra and dynamicsen
dc.typeArticle (peer-reviewed)en
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