Infrared spectroscopy of cold trapped molecular ions using He‐tagging. Issue 6 (21st May 2018)

• Record Type: Journal Article
• Authors: Gerlich, Dieter
• Is Part Of: Journal of the Chinese Chemical Society. Volume 65:Issue 6(2018)
• Page Start: 637
• Page End: 653
• Publication Date: 2018-05-21
• Subjects: cryogenic ion traps -- He tagging -- ion spectroscopy -- linear multipoles -- LIP and LIICG; Chemistry -- Periodicals; Electronic journals; 540.5
• DOI: 10.1002/jccs.201800122
• Languages: English
• ISSNs: 0009-4536

Abstract

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 O2 + 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 C60 + . 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 N2 +, VO +, and H3 + 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–H3 + . In the conclusions, hints to additional applications will be given, emphasizing on the versatility of temperature‐variable ion traps. Abstract : Laser detachment of He from cold ion complexes provides detailed information. A significant step forward was to synthesize such structures inside cryogenic ion traps. The figure shows two IR lines, the smaller one has been measured for D3 + using a method called laser‐induced inhibition of complex growth (LIICG), while the broader one was measured through the predissociation of the He–D3 + complex. The ball shows the He wave function surrounding an H3 + (A″ symmetry, J = 1, Π state, parity f).