A new method for investigating infrared spectra of protonated benzene (C6H7+) and cyclohexadienyl radical (c-C6H7) using para-hydrogen

Abstract

We use protonated benzene (C(6)H(7)(+)) and cyclohexadienyl radical (c-C(6)H(7)) to demonstrate a new method that has some advantages over other methods currently used. C(6)H(7)(+) and c-C(6)H(7) were produced on electron bombardment of a mixture of benzene (C(6)H(6)) and para-hydrogen during deposition onto a target at 3.2 K. Infrared (IR) absorption lines of C(6)H(7)(+) decreased in intensity when the matrix was irradiated at 365 nm or maintained in the dark for an extended period, whereas those of c-C(6)H(7) increased in intensity. Observed vibrational wavenumbers, relative IR intensities, and deuterium isotopic shifts agree with those predicted theoretically. This method, providing a wide spectral coverage with narrow lines and accurate relative IR intensities, can be applied to larger protonated polyaromatic hydrocarbons and their neutral species which are difficult to study with other methods.

The Infrared Spectrum of Protonated Ovalene in Solid Para-Hydrogen and Its Possible Contribution to Interstellar Unidentified Infrared Emission

“…The matrix-isolation system for mid-IR absorption and the p-H 2 converter used in this work have been described elsewhere (Lee et al 2006;Bahou et al 2012Bahou et al , 2014a. A gold-plated flat copper substrate, cooled to 3.2 K with a closedcycle helium refrigerator system (SHI, RDK-415D), served as both the matrix sample substrate and the mirror to reflect the incident mid-IR beam to the detector.…”

“…The bombardment of p-H 2 with electrons produces H 3 + and H, which subsequently react with PAH to form H + PAH and HPAH which are trapped in the p-H 2 matrix. This method has been successfully applied to benzene (C 6 H 6 ) (Bahou et al 2012), naphthalene (C 10 H 8 ) (Bahou et al 2013a), pyrene (C 16 H 10 ) (Bahou et al 2013b), and coronene (C 24 H 12 ) (Bahou et al 2014b) to obtain mid-IR spectra of the protonated species and their neutral counterparts with narrow lines and excellent signal-to-noise ratios. Furthermore, this method does not induce significant fragmentation nor further hydrogenation of PAHs and H + PAHs.…”

FAR ULTRAVIOLET ABSORPTION SPECTRA OF N3AND N2+GENERATED BY ELECTRONS IMPACTING GASEOUS N2

“…The experimental setup was similar to that described in previous literature (Bahou et al 2012(Bahou et al , 2013 for the purpose of measuring the spectra of icy samples irradiated with energetic electrons. A nickel-plated copper plate was utilized as a cold substrate for icy samples.…”

Electronic and vibrational spectra of protonated benzaldehyde-water clusters, [BZ-(H2O)n≤5]H+: Evidence for ground-state proton transfer to solvent for n ≥ 3

“…[3][4][5][6][7][8][9][10][11] Recently, IR and electronic spectra of cold AH + ions have been obtained in cryogenic H 2 and Ne matrices, respectively. 12 Hydration of AH + has a profound impact on their structure and dynamics, as well as their chemical reactivity. Thus, microhydrated clusters of AH + are suitable model systems to study solute-solvent interactions and solvent-induced ion-molecule reactions at the molecular level, 13,14 including proton transfer, which is the most fundamental chemical reaction.…”