Multiphoton dynamics and energetics of halogen containing reagents by mass resolved REMPI and velocity map imaging

Abstract

The research focused on multiphoton dynamics and fragment formation for HBr, DCl, and bromomethanes, using mass resolved multiphoton ionization (MR-MPI) and velocity map imaging (VMI) techniques. Data interpretations were based on analysis of (2+n)REMPI spectra, kinetic energy release spectra (KERs) and angular distributions of ions formed. Experiments for HBr revealed perturbations due to interactions between triplet and singlet states, seen as line-shifts (LS) and line-intensity (LI) alterations in MR-REMPI spectra, and intensity anomalies in VMI data. DCl studies revealed five new Rydberg states, and eight new vibrational states of the ion-pair state, as well as strong perturbation effects between singlet sigma Rydberg and singlet sigma ion-pair state, seen as LS and LI effects, and chlorine isotope shifts. Comparison with analogous data for HCl was performed. Highly perturbed spectral region of four Rydberg states in CH and CD, caused by interaction with a repulsive state, was inspected via multiphoton photodissociation of bromoform in MR-REMPI. In addition to LS and LI effects, linewidth (LW) broadenings, were evident. Four band origins were assigned. A number of Rydberg states of CH3Br in two-photon excitation region of 66 000 – 80 000 cm-1 were resonantly excited. The multiphoton dynamics was explored with both one- and two-colour excitation schemes. One-, two- and three- photon initial excitations were found to form ground state fragments CH3 and Br/Br*, whereas CH3 Rydberg states along with Br/Br* were found to be the major products following three-photon excitations prior to ionization. Interaction between Rydberg and ion-pair states is found to be evident.

Rannsóknirnar fólust einkum í að kanna áhrif fjölljóseindaörvunar á rofferli HBr, DC l og brómometan sameinda með massagreiningu (MR-MPI aðferð) og myndgreiningu (VMI). Túlkun mæligagna fólst í greiningu á fjölljóseindarófum ((2+n)REMPI róf) sem og á hraða- (KERs) og hornháðum dreifimynstrum jóna sem myndast. Athuganir á HBr sýndu truflanir vegna víxlverkana á milli þrístigs- og einstigs-orkuástanda sameindarinnar, sem birtust í formi hliðrunar (LS áhrif) og styrkbreytinga (LI áhrif) litrófslína í MR-REMPI litrófum sem og í formi óreglulegra mynstra í VMI myndum. Samkvæmt DCl mæligögnum fundust fimm ný Rydberg orkuástönd og átta ný titringsástönd jón-para forms sameindarinnar. Sterk víxlverkunaráhrif greindust milli einstigs Rydberg ástanda og jón-para ástandsins sem birtist í formi LS og LI áhrifa og sem samsætuhliðranir. Framkvæmdur var samanburður við sambærileg gögn frá HCl. Óreglulegt mynstur REMPI litrófa fyrir sameindabrotin CH og CD sem mynduðust við fjölljóseindarof bromoforms báru vitni um hraðvirka rofnun fjögurra Rydberg ástanda. LS og LI áhrif sem og breikkun litrófslína báru þessu vitni. Orka viðkomandi ástanda var auðkennd. Fjölmörg Rydberg ástönd CH3Br sameindarinnar voru orkuörvuð á tveggja ljóseinda bylgjutölusviðinu 66 000 – 80 000 cm-1 . Rofferli voru könnuð með aðferðum eins- og tvílita fjölljóseindaörvana. Einnar-, tveggja og þriggja ljóseinda örvanir sameindarinnar leiddu allar til myndunar sameindabrotanna CH3 og Br í grunn-rafeindaástöndum. Meginrofferli sameindarinnar var hins vegar myndun CH3 Rydberg ástanda ásamt bróm frumeindum í kjölfar þriggja ljóseinda örvunarinnar. Vísbendingar um víxlverkun milli Rydberg ástanda og jón-para ástanda fundust.