Infrared spectroscopy of cold trapped molecular ions using He‐tagging

Abstract

This review summarizes experimental activities to study the structure of molecular ions via He tagging. The method is based on the attachment of a weakly bound helium atom to a cold ion followed by laser-induced predissociation (LIP). Since my early involvements (it started in 1977 with a letter from Y.T. Lee), radio frequency (rf ) ion traps and ion guides have been important elements in instruments dedicated to ion spectroscopy. Accumulating ions in a ring electrode trap (RET) and confining them together with the laser-induced photofragments in a long octopole has been demonstrated in 1978 in Berkeley via photodissociation of metastable O 2 + ions. In the early stage of this instrument, as well as in various further developments, supersonic expansions have been used to create weakly bound complexes. An important step forward for ion spectroscopy was to push the conditions of cryogenic ion traps so far that, finally, He atoms could be attached to almost any mass-selected ion of interest, including multiply charged ions and C 60 + . Currently, modern ion storage instruments reach temperatures below 3 K and can be operated at helium densities above 10 16 cm −3 , opening up many avenues of application in spectroscopy, reaction dynamics, and analytical chemistry. In addition to a personal historical review, I discuss recent progress made with new cryogenic ion traps, especially in the field of He tagging. He-M + ions have been formed via ternary association for all kind of M + ions ranging from atoms such as He + , N + , or Fe + via molecules N 2 + , VO + , and H 3 + to various polyatomic ions. The in situ synthesis of tagged ions made unique discoveries possible, such as determining the structure of doubly charged benzene, the first identification of a carrier of diffuse interstellar bands, or the characterization of the fundamental 4 electron 4 center system He-H 3 + . In the conclusions, hints to additional applications will be given, emphasizing on the versatility of temperature-variable ion traps. K E Y W O R D Scryogenic ion traps, He tagging, ion spectroscopy, linear multipoles, LIP and LIICG

Closed Shell Iron(IV) Oxo Complex with an Fe–O Triple Bond: Computational Design, Synthesis, and Reactivity

“…[32,33] To verify the S = 0[ (L)Fe IV (O)] + ground state,w ee mployed gas-phase IR/vis ion spectroscopy. [34][35][36][37][38][39][40][41][42] [*] Dr.E . Andris We thus created al ibrary of candidate structures (more than 450 ligands; cf.…”

Identification of Active Sites and Structural Characterization of Reactive Ionic Intermediates by Cryogenic Ion Trap Vibrational Spectroscopy

“…Ad istribution of ions of different composition, mass and charge state is generated in the ion source region, typicallyb y way of electron impact ionization, laser vaporization, magnetron sputtering, or electrospray ionization. The beam containing ad istribution of ions of different masses and possibly charge states is transferred into the high vacuum chamber and guided into am ass filter.M ass-selected ions are accumulated in the cryogenically cooled ion trap, where they are thermalized closet oa mbient temperature by collisions with ab uffer gas, typicallyH eo rH 2 (D 2 )o ramixture thereof.T oday,i on trap temperatures of < 10 Kc an be routinelya chieved and < 4Kin state-of-the-art instruments, [34] but ion internal temperatures are typicallys lightly higher due to RF heatinga nd/or inefficient collisional cooling. [34,65] After thermalization and tagging, the ions are extracted from the ion trap, focused in time and space, irradiated with at unable IR laser pulse, mass-selected in as ubsequent mass filter,d etected, and the signals are electronically processed.…”

“…[20][21][22][23] Of thesem ethods,c ryogenic ion trap vibrational spectroscopy [20] has emerged as the most generally applicable. [24][25][26][27][28][29][30][31][32][33][34] Cryogenic ion traps [35,36] do not only allow for at hermalization of the trapped ions close to the ambient temperature, buta lso provide an alternative methodf or the formation of messenger-complexes. [37] Separating the cluster formation process( in the ion source region) from the tagging process (in the ion trap region) has far-reaching consequences.…”

Flavinium Catalysed Photooxidation: Detection and Characterization of Elusive Peroxyflavinium Intermediates

“…Next, we have determined structures of the detected intermediates by helium tagging infrared photodissociation (IRPD) spectroscopy. [13][14][15] Thec orrect structures were assigned based on comparison of the experimental data with theoretical IR spectra of possible isomers.W ep resent the results for [1a+ 2H,2 O] + here;t he results for other complexes are shown in the Supporting Information ( Figure S39), as their structures are analogous.…”