The UV spectra of primary, secondary, and tertiary alkyl radicals

Abstract

Gas phase absorption spectra have been measured for one primary, three secondary, and two tertiary alkyl radicals in the 195 to 370 nm wavelength range. Radicals were generated by Hg-photosensitized reactions and observed by modulation spectroscopy. The pattern of bands observed agrees well with ab initio predictions for the 3s, 3p, and 3d Rydberg transitions and can be reproduced by a Rydberg formula using experimental vertical ionization potentials and normal quantum defects. Oscillator strengths and condensed phase blue shifts are consistent with the Rydberg assignment. A similarity with the spectra of primary, secondary, and tertiary amines is noted.

Ultraviolet photodissociation dynamics of the n-propyl and i-propyl radicals

“…21 Another study on the UV absorption spectrum of i-propyl was performed by Munk et al in 1986, 23 identifying two distinct bands at 233 nm and 205 nm. The UV absorption spectra of a series of primary, secondary, and tertiary alkyl radicals were reported by Wendt and Hunziker, 24 showing the broad absorption peaks of i-propyl at 270 nm, 236 nm, and 207 nm, respectively. Theoretical assignments of the UV absorption spectra of the alkyl radicals were limited.…”

Excited-state decay of hydrocarbon radicals, investigated by femtosecond time-resolved photoionization: Ethyl, propargyl, and benzyl

“…The lowest electronically excited state is the 2 2 AЈ state, nominally the 3s Rydberg state, the corresponding absorption band with a maximum at 246 nm being broad and unstructured. 18,19 If this state decays by IC to the electronic ground state as suggested, the subsequent dissociation to C 2 H 4 + H is expected to proceed within some picoseconds, as calculated by statistical theories 20,21 based on a heat of reaction, ⌬ R H ‫ؠ‬ = 159 kJ/ mol and a reverse barrier of around 10 kJ/ mol. However, time-resolved detection of the H-atom photofragment 11 yielded a rate constant on the order of 10 7 s −1 .…”

“…From the steadystate UV spectrum recorded in our laboratory we conclude that n-propyl is generated by 250 nm excitation of n-propyl nitrite. It is then excited by a second 250 nm photon to the 3s state, 18,19 the lifetime of which is probed by either 280 nm or 800 nm ionization. Since the radical was produced by photolysis in the ionization region, again only a limited analysis of the data is possible.…”

Br ( P j 2 ) atom formation dynamics in ultraviolet photodissociation of tert-butyl bromide and iso-butyl bromide

“…The tert-C 4 H 9 fragment is also ionized efficiently in the 234 and 265 nm regions, presumably via ͑1+1͒ REMPI process. 20 The wavelengths were chosen as 233.80 and 265.00 nm, which is comparable to those of bromine atoms. The generated ions were extracted and accelerated by the electrostatic immersion lens and projected onto a 2D detector composed with a microchannel plate ͑MCP͒/phosphor screen and a charge-coupled device ͑CCD͒ camera.…”