The Infrared Spectrum of Protonated C₇₀

Abstract

With the detection of C 60 , C 70 , and + C 60 in the interstellar medium, fullerenes are currently the largest molecules identified in space. The relatively high proton affinities of C 60 and C 70 support the hypothesis that protonated fullerenes may also be abundant in the interstellar matter. Here, we present the first experimental vibrational spectrum of C 70 H + , recorded in the gas phase. The attachment of a proton to C 70 causes a drastic symmetry lowering, which results in a rich vibrational spectrum. As compared to C 60 , where all C-atoms are equivalent due to the icosahedral symmetry, C 70 belongs to the D 5h point group and has five nonequivalent C-atoms, which are available as protonation sites. Combined analysis of the experimental spectrum and spectra computed at the density functional theory level enables us to evaluate the protonation isomers being formed. We compare the IR spectra of C 60 H + and C 70 H + to IR emission spectra from planetary nebulae, which suggests that a mixture of these fullerene analogs could contribute to their IR emission.

Synthesis and Spectroscopy of Buckminsterfullerene Cation C60+ in a Cryogenic Ion Trapping Instrument

“…In addition, C 60 was detected earlier [19,20] in various nebulae (see [21] and references therein) by emission of infrared radiation. Recently, laboratory infrared spectra of C + 60 , C 60 H + , and C 70 H + were also reported and compared with observations [22][23][24].…”

Laboratory IR Spectra of the Ionic Oxidized Fullerenes C60O+ and C60OH+

“… 11 , 48 We noticed earlier that this feature resembles the spectral characteristics of protonated C 60 and C 70 . 19 , 20 We suggested that a mixture of these protonated fullerenes, perhaps together with radical cation fullerenes, may give rise to this emission feature. Here, we add the newly recorded spectra of the oxidized fullerene analogues to the comparison.…”

“…The APCI source is particularly suitable for studying apolar substances such as PAHs 40 and fullerenes. 19 , 20 The DIP inlet replaces the spray nebulizer on the standard Bruker APCI ion source. The solid sample is placed on the tip of a single-use glass tube of the DIP, where it is heated and sublimates into the APCI source chamber.…”

“…Ions are produced in an atmospheric pressure chemical ionization (APCI, Bruker APCI II) source using a direct insertion probe (DIP, Bruker DP) assembly. The APCI source is particularly suitable for studying apolar substances such as PAHs and fullerenes. , The DIP inlet replaces the spray nebulizer on the standard Bruker APCI ion source. The solid sample is placed on the tip of a single-use glass tube of the DIP, where it is heated and sublimates into the APCI source chamber.…”

“…Protonated, hydrogenated, and oxidized fullerenes have therefore often been hypothesized (also by Kroto himself 14 ), as well as some metallofullerenes. 15 Laboratory investigations aiming to support astronomical searches have indeed been reported for hydrogenated 16 , 17 and protonated 18 − 20 fullerenes.…”