IUPAC Critical Evaluation of Thermochemical Properties of Selected Radicals. Part I

Abstract

This is the first part of a series of articles reporting critically evaluated thermochemical properties of selected free radicals. The present article contains datasheets for 11 radicals: CH, CH 2 (triplet), CH 2 (singlet), CH 3 , CH 2 OH, CH 3 O, CH 3 CO, C 2 H 5 O, C 6 H 5 CH 2 , OH, and NH 2. The thermochemical properties discussed are the enthalpy of formation, as well as the heat capacity, integrated heat capacity, and entropy of the radicals. One distinguishing feature of the present evaluation is the systematic utilization of available kinetic, spectroscopic and ion thermochemical data as well as high-level theoretical results.

Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study

“…Given the non-bonding nature of the p x/y highest occupied molecular orbital (HOMO) in C 2 H 5 X, Franck-Condon arguments would suggest that 118 nm photoionization of the jet-cooled parent molecule will favour formation of C 2 H 5 X + ions in the ground (v = 0) vibrational level of the X 1 A (and X 2 A) states. 60 This behaviour was suggested previously by Xu et al 33 , and is also consistent with the reported He I photoelectron spectrum. 53, 54 The theoretical ranges of internal energies accessible to the nascent parent ions and to the excited-state ions created through absorption of a second 266 nm or 355 nm photon are indicated on 65 Figure 2 by the shading above each energy level.…”

“…The 118 nm and residual 355 nm light were not separated before entering the imaging chamber, and in some of the experiments the latter was used to effect photolysis of the parent cation of interest. In all 60 other 'two-laser' experiments, the requisite UV photolysis light (in the wavelength range 236-266 nm) was produced using a tuneable, frequency-doubled, pulsed dye laser (Sirah Cobra Stretch, 7 ns pulse, laser energy 0.4 to 1 mJ/pulse in a 11 mm 2 spot size in the interaction region, Δν ≈ 0.3 cm -1 ) which was 65 pumped by the third harmonic of a Nd:YAG laser (Continuum Surelite II, 200 mJ per 7 ns pulse). All laser beams were linearly polarised, with their respective electric field vectors, , aligned parallel to the plane of the imaging detector.…”

“…In principle, relative branching ratios can be obtained directly from the fragment peak intensities in the TOF mass spectra, but such analyses are complicated by possible unimolecular decay of internally excited 60 primary fragments (e.g. 33 .…”

“…[19][20][21][22]27 The alternative CX bond fission 55 channel yielding CH 3 + X + fragments opens at higher excitation energies. 18 The observed fragmentation behaviours of both neutral and cationic methyl halide species have been rationalised in terms of the excited electronic states accessible upon photoexcitation, and the way in which their respective potential 60 energy surfaces (PESs) correlate with the available dissociation limits. The ground ( 2 E 3/2 ) and first excited ( 2 E 1/2 ) states of CH 3 X + correlate with CH 3 + + X products.…”

Enthalpies of Formation and Bond Dissociation Energies of Lower Alkyl Hydroperoxides and Related Hydroperoxy and Alkoxy Radicals

“…Alkoxy Radicals. In view of the paucity of consistent and reliable data for the lower alkoxides, R, required for the computation of bond dissociation energies (see below), a series of isodesmic reactions were constructed on the basis of principles similar to those outlined above and using the Ruscic et al 47 value for methoxy of +21.0 ( 2.1 kJ mol -1 to "anchor" the calculations. The results, Table 4, are in moderate agreement with literature values; if a lower value of 17.2 kJ mol -1 is adopted, 48 then all the values in Table 4 are lowered in energy by ≈4 kJ mol -1 .…”