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High-resolution electron spin resonance (ESR) spectrum of ethyl radicals isolated in solid parahydrogen (>99.5 mol %) has been measured in the temperature range between 3.1 and 6.7 K. This study was carried out by UV photolysis of ethyl iodide doped in solid parahydrogen. Although ESR linewidth of the spectrum is broadened due to anisotropic terms of hyperfine interactions, the linewidth measured in parahydrogen remains comparable to that of the isotropic spectrum measured in liquid ethane [R. W. Fessenden, J. Chem. Phys. 37, 747 (1962)]. Small splittings were found in the resolved ESR signals and assigned as ethyl radicals with A(A′,A″) and E(E′,E″) symmetries, respectively. The ratio in the ESR intensities is not proportional to that of the degeneracy of each symmetry but varies as a function of temperature. We measured the signal intensities as a function of temperature and determined the rotational energy level splitting of methyl groups between the lowest with the A(A′,A″) symmetry and the second-low...

We report results on the photodissociation dynamics of the ethyl radical, C2H5. A beam of internally cold radicals is generated by supersonic jet flash pyrolysis of ethyl iodide or n-propylnitrite, respectively. Upon excitation into the A 2A13s Rydberg state ethyl dissociates, presumably on the ground-state surface, into ethylene and a hydrogen atom that is detected by time-resolved photoionization. By varying the excitation energy between 264 and 245 nm, microcanonical rates are obtained as a function of excitation energy. The reaction rates are on the order of 107 s−1, several orders of magnitude slower than expected from simple Rice–Ramsperger–Kassel–Marcus calculations.

Both spin–orbit states of C2H5I+, the X1 2E1/2 and the X2 2E1/2 electronic states, are studied by one‐color two‐photon ionization of ethyl iodide, utilizing the zero kinetic energy pulsed field ionization (ZEKE‐PFI) photoelectron technique. Compared with conventional photoelectron data the two‐photon spectra exhibit a more extensive vibrational structure mainly involving the C–I stretching and the C–C–I bending modes. This additional vibrational excitation in the two‐photon spectra is discussed in terms of mode selective resonance enhancement by the dissociative A‐state continuum. Accurate values for the vibrational frequencies and the ionization energies are obtained. The appearance of nontotally symmetric modes in the two‐color ZEKE spectra is reported.

Photodissociation dynamics of ethyl iodide in the A band has been investigated at several wavelengths between 245 and 283 nm using resonance-enhanced multiphoton ionization technique combined with velocity map ion-imaging detection. The ion images of I, I-*, and C2H5 fragments are analyzed to yield corresponding speed and angular distributions. Two photodissociation channels are found: I(5p P-2(3/2))+C2H5 (hotter internal states) and I-*(5p P-2(1/2))+C2H5 (colder). In addition, a competitive ionization dissociation channel, C2H5I++h nu -> C2H5+I+, appears at the wavelengths < 266 nm. The I/I-* branching of the dissociation channels may be obtained directly from the C2H5+ images, yielding the quantum yield of I-* about 0.63-0.76, comparable to the case of CH3I. Anisotropy parameters (beta) determined for the I-* channel remain at 1.9 +/- 0.1 over the wavelength range studied, indicating that the I-* production should originate from the (3)Q(0) state. In contrast, the beta(I) values become smaller above 266 nm, comprising two components, direct excitation of (3)Q(1) and nonadiabatic transition between the (3)Q(0) and (1)Q(1) states. The curve crossing probabilities are determined to be 0.24-0.36, increasing with the wavelength. A heavier branched ethyl group does not significantly enhance the I(5p P-2(3/2)) production from the nonadiabatic contribution, as compared to the case of CH3I. (c) 2007 American Institute of Physics.

A series of peaks in the Raman spectra of gaseous CH3CH3, CH3CH2Cl, CH3CH2Br, CH3CD2Br, CD3CH2Br, CD3CD2Br, CH3CH2I, CH3CD2I, and CD3CH2I have been observed and assigned to the torsional overtones, (Δν = 2) of the methyl group. From these spectroscopic data, barriers to internal rotation have been calculated for the ethyl halides. For the compounds where the barriers are accurately known from previous work, the values obtained in this study agree quite well. The value for the internal rotational barrier in ethyl iodide is 3.67 ± 0.01 kcal/mole, which is considerably higher than the value previously reported from microwave studies. It is shown that Raman spectroscopy can be a convenient technique for obtaining torsional barrier heights when one uses the Δν = 2 quantum jumps of the torsional motion.

Precision optical interferometric measurements at high pressures have been made on twelve liquids. The liquids studied are chloroform, carbon disulfide, o‐xylene, m‐xylene, 1‐3‐5‐trimethyl benzene, cumene, methyl cyclohexane, ethyl bromide, ethyl iodide, isobutyl alcohol, ethyl acohol, and deuterium oxide. The piezo‐ and elasto‐optic properties of these liquids are found to be similar to those of other liquids described in Papers I and II of this series. For all these liquids, the data reveal pronounced nonlinear piezo‐optical (Δn vs P) behavior, but linear elasto‐optical (Δn vs e, when e is the Eulerian strain) relationship. Thus, the Eulerian representation of strain is advantageous in describing the elasto‐optic behavior of liquids, irrespective of the shape, size, and composition of the molecules of the liquid. The linear relationship between Δn and Eulerian strain can be used to discriminate between the various equations of state. It may also provide a simple empirical expression for the computation of density from the accurately measured values of the changes in refractive index of liquids. The various expressions prevalent in the literature for the relationship between refractive index and density were analyzed by least‐squares analysis technique. It is shown that the Drude and Lorentz–Lorenz equations (which are most widely used in the literature on such studies) give either too low or too high values of Δn. Kirkwood–Brown and Omini equations which were derived using detailed statistical mechanical approach, appear to yield values in moderately good agreement with experimental values.

The kinetics of the reaction between EtI and HI have been studied in the temperature range 263° to 303°C using a spectrophotometric technique for the determination of I2. The mechanism obeyed is the following: I2⇌2I, KI2I+EtI⇌ lim 21Et+I2,Et+HI⇌ lim 43EtH+I,, which has the rate law (neglecting Step 4): d(I2)dt=k1k3KI212(EtI)(HI)(I2)12k2(I2)+k3(HI).. Decomposition of EtI by unimolecular elimination of HI is negligible.A differential method was employed to determine the rate constants k1 and the ratio k2/k3. The Arrhenius parameters of these constants were evaluated experimentally and combined with known thermodynamic data to give the parameters of the individual constants k2, k3, k4. As with other I2 molecule systems, the A factors of Reactions (1) and (4) are high, being approximately equal to collision frequencies.With the assumption E2=0.2 kcal and the experimental activation energy E1, the C–I bond‐dissociation energy in EtI is found to be 52.9±1.0 kcal at 25°C. The heat of formation of the ethyl radi...

The absorption spectra of the ethyl and higher halides have been examined in the region 2000–1000A. It has been found that they are essentially similar to those of the methyl halides. The ionization potentials of ethyl iodide are given as 9.30 and 9.88 volts and those of ethyl bromide as 10.24 and 10.56 volts. The ionization potentials of the higher halides cannot be determined exactly because of the presence of continuous absorption from the C–C and C–H bonds, and of the diffuseness of the bands themselves. However there is strong evidence that the ionization potentials of consecutive members of the homologous series diminish asymptotically to a limiting value, the diminution from methyl to ethyl being by far the greatest. A comparison of the way the ionization potentials diminish and the dipole moments of the carbon‐halogen bonds increase as we ascend the homologous series indicates a definite connection between the two phenomena.

The addition of HI to C2H4 yields C2H5I at low temperatures and C2H6+I2 at higher temperatures. From 289° to 331°C the rate law is mixed—second order with C2H6+I2 as products. The rate is independent of added I2 and has a specific rate constant k2 (units, liter/mole‐sec): logk2=8.52−(28900/4.575T). The pyrolysis of C2H5I from 330° to 392°C goes by a first‐order process to C2H4+C2H6+I2. The first‐order rate constant is given by (units, sec—1): logku=13.66−(50000/4.575T).If it is assumed that both processes have the same rate determining step, namely the reversible dissociation of C2H5I, they yield an equilibrium constant in good agreement with independently calculated values of Keq for this dissociation. Under these conditions k1, the specific rate constant for the unimolecular split of C2H5I into C2H4+HI is given by ku/2. Arguments are presented to show that this common path involves the four‐center molecular transition state rather than a radical disproportionation. The latter, however, may account for as much as 20% of the pyrolysis at 392°C.

Benzene, naphthalene, related hydrocarbons and some of their derivatives act as optical sensitizers towards the decomposition of alkyl iodides in hexane solution. Within this group, the sensitizing power of a substance towards an acceptor runs parallel with the ability of the acceptor to quench the fluorescence of the sensitizer; this is demonstrated quantitatively and in detail. The quantum yield of the naphthalene‐sensitized decomposition of ethyl iodide follows an equation of the form 1/φ=a+b(1/[EtI]), and detailed analysis of the quenching and sensitization shows that while sensitization and fluorescence are alternative processes, they are not completely reciprocal, in that more molecules may sensitize than may potentially fluoresce. All of the observed features of the sensitization are consistent with its being the result of a resonative transfer of energy at collision from the excited sensitizer to the acceptor.

The existence of the isomer 130Im (9.2 min) has been established by the growth of the gamma‐ray spectrum of the 130I ground state following neutron irradiation of 129I, and also by the incorporation of 130I into organic combination as a result of the isomeric transition of I2(130Im) dissolved in n‐hexane. The isomer decays to the ground state by a highly converted isomeric transition with a 0.77 probability and to the 0.54‐MeV level of 130Xe by beta emission with 0.23 probability. The cross‐section ratio, σ(130Im)/σ(130I), for production of the isomers from 129I by pile neutrons is about 2.0. The fraction of the isomeric transition events which result in organic incorporation of the 130I daughter in solutions of I2(130Im) in n‐hexane, or in solutions of RI(130Im) in ethyl iodide, is about 0.40.

The organic retentions for (d,p), (n,2n), and (γ,n) activation of iodine in liquid methyl and ethyl iodide, containing added iodine, have been found to be equal to the retentions observed in radiative neutron capture. This demonstrates that the chemical effects are independent of the recoil energy of the activated nucleus, of the mode of nuclear formation, and of variation of fragmentation effects within the recoil track. In the absence of scavenger iodine, the increase in retention due to radiation damage is less than 10 percent in all cases studied.

The photochemical investigation of the decompositions of diethyl zinc and diethyl mercury has established that the products in each case consist principally of ethane, ethylene, and butane, with smaller amounts of hydrogen and butylene. The composition of the product varies with the alkyl, but does not change markedly with temperature from 45° to 250°. An examination of the effects of varying the concentration, intensity of radiation, packing of reaction vessel, and inert gas pressure leads to the conclusion that butane is formed by the combination of two ethyl radicals produced in the primary process, while ethane and ethylene arise from a reaction between ethyl radicals and metal alkyl molecules. The reaction between ethyl radicals and hydrogen becomes measurable at about 160°, and by analogy with the corresponding process with methyl radicals may be assigned an activation energy of 9±2 kcal. The reaction C2H5+H=2CH3 proceeds rapidly at 100°. The investigation of the photolysis of ethyl iodide in the presence of mercury vapor and the mercury photosensitized hydrogenation of ethylene supports the conclusions based on the metal alkyl studies.

The infrared absorption spectra of ethyl chloride, ethyl bromide and ethyl iodide have been determined with a prism spectrometer between 1.5μ and 15μ. Eight experimentally observed fundamental frequencies have been selected which, together with their first harmonics and simple combinations, are shown to account for the entire spectrum. A type of vibration between atom pairs believed to represent the important feature of the motion of the atoms is suggested for each of these fundamentals. The shifts in the absorption maxima produced by the substitution of the different halogens together with absorption and Raman data of related compounds are used in selecting these types of vibration. The bearing of these hypotheses on problems in chemical kinetics is discussed.

The photolysis of C2H5I and C2D5I have been investigated at 2537 and 2288 A in the presence of thermal alkyl radical scavengers such as O2 or I2. The ethane (quantum yields at 2537 A: φC2H6=0.82×10−3, φC2D6=0.29×10−3) formed in such mixtures can be entirely ascribed to abstraction of an H (or D) atom by a ``hot'' ethyl radical formed in the primary dissociation of ethyl iodide. The differences in quantum yield between C2H6 and C2D6 are in part ascribed to a difference in the partitioning of the excess energy (∼30–40 kcal) carried over from the primary process into vibrational and translational modes. When C2D5I or C2H5I is photolyzed in the presence of a cyclo‐C6H12–cyclo‐C6D12–O2 mixture (1:1:0.1), or of a cyclohexane‐1,1,2,2,3,3,‐d6–O2 mixture, the relative probability for abstraction of an H atom vs that for abstraction of a D atom (πH/πD) is equal to 1.5±0.1. The latter value shows little dependence on a change in wavelength and is also not affected when unreactive gases are added to the reaction mixt...

The pyrolysis of tagged ethyl iodide has been studied in the presence of the radical scavenger toluene in a flow system. The rate constants for the formation of C2H4(kD), C2H6(kS), and bibenzyl have been determined as a function of the contact time, toluene pressure (2–18 mm Hg), and C2H5I pressure PE(0.6–40×10−3 mm Hg) at 774°K. It is concluded that kD≈k1 and kS≈k2 at low kiPE, where C2H5I→ lim k1C2H4+HI,C2H5I→ lim k2C2H5+I. The first reaction appears to be first order at 14 mm Hg of toluene pressure with a high‐pressure Arrhenius rate constant k1∞ of 1.27×1014 exp (−52.8×103/RT) sec−1. The second reaction is not first order at any pressure, but by extrapolation k2∞ was estimated to be 4.5×1013 exp (−50×103/RT) sec−1.The RRKM theory was used to fit the pressure dependence of k1 and k2 in the approximation that the same degrees of freedom are active in the energized molecule A* for both reactions. The disagreement between theory and experiment could be the result of fewer of the rotational degrees of free...

A yellow color is produced when two colorless pure liquids, α‐chloronaphthalene and ethyl iodide, are mixed, although no chemical reaction occurs. Spectroscopic examination reveals that the lowest singlet→triplet absorption band of the naphthalene molecule is greatly enhanced in intensity in the presence of the iodide, and that the development of this absorption band is responsible for the color effect. The process is interpreted in terms of a collisional perturbation of spin‐orbital coupling in the π‐electron orbitals of the naphthalene. The significance of this phenomenon in several topics in spectroscopy and chemistry is discussed. In particular, the molecular mechanism of heavy atom quenching of fluorescence by foreign species is resolved. A novel Beer's law anomaly is predicted for intercombinations.

The work reported here is an application of free precession or ``spin echo'' techniques in nuclear magnetic resonance to a study of the properties of liquids under high pressure. The proton relaxation time T1 was measured as a function of pressure, over the range 1 to 10 000 atmospheres, for six liquids: water, n‐pentane, n‐hexane, toluene, ethyl iodide, and methyl iodide. In addition to the relaxation time, the normalized values D(P)/D(1) of the self‐diffusion constant were measured as a function of pressure for water and methyl iodide.In each liquid T1 decreases with increasing pressure. However, comparison of the observed variation of T1 with pressure with Bridgman's data on the variation of viscosity η with pressure shows in all cases (except that of methyl iodide for which no viscosity data are available) that T1 is not simply proportional to 1/η, but instead T1η increases with pressure. Similarly, for water and methyl iodide, the diffusion constant D varies in such a way that T1/D increases with pre...

The products of the reactions of sodium vapor with methyl and ethyl iodide vapors have been analyzed. It has been found that in the reaction with methyl iodide the principal product is ethane, but considerable amounts of methane, ethylene, and hydrogen are also formed. With ethyl iodide the principal product was butane, with lesser amounts of ethane, ethylene, methane, and hydrogen. It was also noted that in the latter system considerable amounts of propane appeared which could be accounted for as a pyrolysis product of the butane formed. The results have been compared with those obtained by others with similar systems and with the results obtained in the photolyses of mercury dimethyl and mercury diethyl. It is concluded that at low temperatures the dominant reaction for both ethyl and methyl radicals is for two to combine to form a saturated hydrocarbon. At higher temperatures, disproportionation reactions and reactions of the radicals with other molecules must be taken into account and eventually become the dominant reactions.

The extinction coefficient of the singlet‐triplet transition of alpha‐chloronaphthalene in ethyl iodide is found to increase almost linearly with the density of the compressed mixture. Study of a 1 : 2 volume ratio of these components over a pressure range from 1 to 3644 atmospheres resulted in about a two fold increase in light absorption, with little other changes in band envelope. No increase in absorption coefficient was obtained for pure liquid alpha‐chloronaphthalene subjected to comparable increase in hydrostatic pressure. The increase in extinction coefficient is attributed to the increase in collisional frequency resulting from the increase in concentration of the constituents and the corresponding decrease in the liquid ``cage'' dimensions with increased density.

The CO2 laser irradiation of ethyl iodide in the pressure range 7–80 torr has been thoroughly investigated. The results can best be described as a laser driven thermal explosion (LDTE). The LDTE is characterized by a high temperature zone in which the laser energy is converted to heat. If the temperature of this zone is high enough, reaction begins. Higher absorptivity of the products leads to thermal instability and explosion. Temperatures in the system have been measured and adequately account for the entire reaction. A computer simulation based on purely thermal reaction confirms the conclusion that the reaction is entirely thermal. The importance of the high temperature reaction zone in infrared irradiation experiments is discussed.