Dynamics and energetics relevant to multiphoton excitation via Rydberg and Ion-pair molecular and atomic states

Abstract

The research focused on the multiphoton dynamics and energetics for the HI, CH3I, CH3Br, and C2H2 molecules by using one- and two-color mass-resolved (MR) resonance enhanced multiphoton ionization (REMPI) and/or velocity map imaging (VMI) in association with REMPI. MR-REMPI experiments for HI revealed new Rydberg and ion-pair states as well as perturbation cases due to interactions between electronic states, which appeared as line-shift (LS), line-intensity (LI), and line-width (LW) alternations in REMPI spectra. CH3I multiphoton dynamic studies by VMI-REMPI revealed the formation of excited Rydberg states of iodine atoms (I**) along with CH3(X) to be the significant formation channel in the two-photon excitation region of 55 700 to 70 000 cm-1 . Rather unusual observation, this was found to occur via three-photon excitation to superexcited molecular states (CH3I # ). Iodine atomic lines in REMPI spectra for I+ signals in the two-photon excitation region of 76 680 -82 620 cm-1 for CH3I and HI revealed autoionization of superexcited iodine atoms (I # ). Several new spectral peaks were assigned, and the autoionization mechanisms were identified. Two-color MR-REMPI / pump and probe experiments were designed and developed to perform photofragmentation experiments and spectra analysis of fragment species. The technique was successfully applied for CH3Br. Further work is in preparation. Multiphoton breakdown of acetylene (C2H2) was studied by VMI-REMPI via molecular Rydberg states. The number of photofragmentation channels, involving the formation of ground and excited state fragments for two-, three- and four-photon excitations prior to photoionization, were identified.

Rannsóknirnar fjölluðu um ljósrof og orkueiginleika sameindanna HI, CH3I, CH3Br og C2H2. Ýmist var notast við einn eða tvo lasergeisla við ljósörvanir og fleiri en ein ljóseind nýttust til að rjúfa og/eða jóna sameindirnar eða sameindabrot þeirra. Annars vegar var notast við massagreiningu jóna (aðferð MR-REMPI), hins vegar við myndgreiningu jónadreifinga (VMI-REMPI). MR-REMPI mælingar HI leiddu til auðkenningar nýrra orkuástanda sameindarinnar sem og orkuvíxlverkana innan sameindarinnar. Orkuvíxlverkanir birtast í formi bjögunar/óreglu á mældum litrófum (REMPI-litróf). VMI-REMPI mælingar á CH3I leiddu í ljós ýmsa roferla. Einn, fremur óvenjulegur, var þó yfirgnæfandi. Hann fólst í myndun orkuríkra joðatóma (I**) og sameindabrotsins CH3 í kjölfar myndunar óstöðugra ofurorkuríkra sameinda (CH3I #) við þriggja ljóseinda örvun. Joð-atóm litrófslínur í REMPI rófum fyrir CH3I og HI báru með sér að sjálfjónun (e. autoionization) óstöðugra ofurorkuríkra atóma (I#) ætti sér stað. Ýmsar nýjar joðatóm litrófslínur voru auðkenndar. Aðstaða til að framkvæma rannsóknir á rofferlum og orkueiginleikum sameindabrota með tvílita ljósörvun (MR-REMPI) var hönnuð og þróuð. Aðferðin var notum með jákvæðum árangri við mælingar á CH3Br. Frekari vinnsla er enn í gangi. Fjölljóseindarof acetylene (C2H2) sameindarinnar var rannsakað með VMI-REMPI aðferðinni. Fjölmargir rofferlar, í kjölfar tveggja-, þriggja- og fjögurra- ljóseinda örvana, sem leiddu til myndunar ýmissa sameindabrota og frekari jónunnar fundust og voru auðkenndir.