Ultraviolet absorption spectrum of the benzyl cation observed by the pulse radiolysis of benzyl chloride

Electronic absorptions of the benzylium cation

“…Although, both Bz + and Tr + are predicted to have distinctive electronic transitions in the visible and ultraviolet (UV) regions, until recently, only rather broad, structureless electronic absorptions had been observed for C 7 H 7 + cations in the solution phase, Ar matrix environment, and in ion traps. [5][6][7][8][9][10] Moreover, these studies are characterised by significant differences in reported band positions and assignments. For example, Ar matrix studies with benzyl chloride a) Electronic mail: evanjb@unimelb.edu.au.…”

On the Benzylium/Tropylium Ion Dichotomy: Electronic Absorption Spectra in Neon Matrices

“…The first reported spectrum of Tr + revealed a broad ultraviolet (UV) absorption in a low‐pH water solution of its bromide salt 8. The following decades produced a sparse number of additional experimental results on the excited states of the cations in question, including photoelectron spectroscopy for Tr + ,9 whereas direct absorption in acidic solutions,10 pulse radiolysis,11, 12 and laser flash photolysis13 in liquids, as well as a photoionization study in an argon matrix14 were used to determine the electronic transitions of Bz + . Despite these efforts, the spectroscopic data for C 7 H 7 + is ambiguous.…”

On the Benzylium/Tropylium Ion Dichotomy: Electronic Absorption Spectra in Neon Matrices

“…The most plausible results were obtained in a pulse radiolysis experiment on liquid BzCl containing O 2 , ethanol, or pyrrole as radical or ion interceptors; they quenched the transient absorptions to a different extent. [11] Two broad, structureless absorptions of Bz + with maxima at 304 (strongest) and 500 nm have been reported. The spectrum agrees well with the present neon matrix data; however, neon is a less perturbing environment and reveals well-resolved vibrational structure.…”

“…Furthermore, the reported UV spectrum of Tr + in strong acidic solutions has a maximum at 275 nm. [8,20] UV electronic transitions of Bz + have been studied in the past using different methods: low-pH solutions, [10] pulse radiolysis, [11,12] laser flash photolysis, [13] and photoionization in an argon matrix. [14] The spectra obtained did not agree with each other.…”

“…The first reported spectrum of Tr + revealed a broad ultraviolet (UV) absorption in a low-pH water solution of its bromide salt. [8] The following decades produced a sparse number of additional experimental results on the excited states of the cations in question, including photoelectron spectroscopy for Tr + , [9] whereas direct absorption in acidic solutions, [10] pulse radiolysis, [11,12] and laser flash photolysis [13] in liquids, as well as a photoionization study in an argon matrix [14] were used to determine the electronic transitions of Bz + . Despite these efforts, the spectroscopic data for C 7 H 7 + is ambiguous.…”