Elucidating Initial Dissociation Processes in Energetic Molecules Through Femtosecond Pump-probe Spectroscopy

Abstract

UnderstandingÊtheÊinitialÊdissociationÊmechanismsÊofÊisolatedÊenergeticÊmoleculesÊisÊimportantÊforÊdevelopingÊnovelÊenergeticÊmoleculesÊthatÊpossessÊtailoredÊpropertiesÊsuchÊasÊhighÊenergyÊdensityÊandÊtheÊabilityÊtoÊdetonateÊuponÊphotoinitiation.ÊInitialÊbondÊcleavageÊeventsÊinÊisolatedÊenergeticÊmoleculesÊcanÊproceedÊfromÊtheirÊelectronicallyÊexcitedÊstatesÊandÊmolecularÊionsÊviaÊnon-radiativeÊrelaxationÊthroughÊconicalÊintersectionsÊonÊexcitedÊstateÊpotentialÊenergyÊsurfacesÊonÊtheÊultrafastÊtimescaleÊofÊfemtosecondsÊ?Êpicoseconds.ÊTheÊproposedÊworkÊwillÊinvestigateÊtheseÊprocessesÊinÊisolatedÊenergeticÊmoleculesÊandÊtheirÊionsÊthroughÊfemtosecondÊtime-resolvedÊpump-probeÊmeasurementsÊandÊcomplementaryÊtheoreticalÊcalculations.ÊInÊorderÊtoÊunderstandÊtheÊroleÊofÊmolecularÊstructureÊinÊdeterminingÊdissociationÊdynamicsÊthroughÊspecificÊpathways,ÊaÊseriesÊofÊexperimentsÊwillÊbeÊperformedÊonÊthreeÊmolecularÊfamiliesÊcontainingÊnitroÊgroupsÊandÊnitrogenÊheterocycles,ÊwhichÊareÊcommonÊmoietiesÊinÊenergeticÊmolecules.ÊTheseÊvolatileÊcompoundsÊwillÊbeÊdirectlyÊintroducedÊintoÊtheÊextractionÊregionÊofÊaÊlinearÊtime-of-flightÊmassÊspectrometer,ÊwhereÊaÊpairÊofÊtime-delayedÊfemtosecondÊlaserÊpulsesÊwillÊionizeÊtheÊmoleculeÊandÊprobeÊtheÊsubsequentÊdynamicsÊofÊtheÊradicalÊcations.ÊToÊstudyÊultrafastÊdissociationÊprocessesÊinÊnonvolatileÊenergeticÊmolecules,ÊanÊinstrumentÊcombiningÊfemtosecondÊlaserÊdesorptionÊwithÊtime-resolvedÊopticalÊexcitationÊforÊtransientÊspectroscopicÊandÊmassÊspectrometricÊdetectionÊwillÊbeÊconstructed.ÊFollowingÊaÊseriesÊofÊexperimentsÊtoÊoptimizeÊtheÊdesorptionÊconditionsÊforÊminimizingÊfragmentationÊofÊtheÊdesorbedÊmolecules,Êtime-resolvedÊdesorb-pump-probeÊexperimentsÊwillÊbeÊperformedÊonÊnitroaromatic,Êtetrazole,ÊandÊfurazan-basedÊenergeticÊmolecules.ÊForÊallÊofÊtheseÊmolecules,ÊtheÊobservedÊdynamicsÊwillÊbeÊinterpretedÊbyÊcalculatingÊtheÊrelevantÊpotentialÊenergyÊsurfacesÊofÊneutralÊexcitedÊstatesÊandÊmolecularÊionsÊwithÊtheÊdensityÊfunctionalÊtheoryÊ(DFT),Êtime-dependentÊDFTÊ(TDDFT),ÊandÊequation-of-motionÊcoupledÊclusterÊsinglesÊandÊdoublesÊ(EOMCCSD)Êapproaches,ÊasÊwellÊasÊtheÊlocationsÊofÊconicalÊintersectionsÊwithÊtheÊcompleteÊactiveÊspaceÊself-consistentÊfieldÊ(CASSCF)Êmethod.ÊItÊisÊexpectedÊthatÊtheÊproposedÊtime-resolvedÊexperimentsÊwillÊrevealÊdissociationÊdynamicsÊinÊenergeticÊmoleculesÊonÊaÊsignificantlyÊfasterÊtimescaleÊthanÊachievableÊwithÊcurrentÊinstrumentation.

Document Details

• Document Type: DoD Grant Award
• Publication Date: Mar 11, 2019
• Source ID: W911NF1910099

Entities

People

• Katharine Moore Tibbetts

Organizations

• Army Contracting Command
• United States Army
• Virginia Commonwealth University