The electron paramagnetic resonance of a number of alternant methylene compounds has been observed, and zero-field splitting parameters have been obtained. The results are D=0.6276±0.0002 cm−1 and E=0.0000±0.0008 cm−1 for H–↑C↑–C≡C–H,D=0.6263±0.0002 cm−1 and E=0.0000±0.0008 cm−1 for H–↑C↑–C≡C–CH3,D=0.5413±0.0004 cm−1 and E=0.0035±0.0003 cm−1 for H–↑C↑–C≡C–C6H5,D=0.6087±0.0001 cm−1 and E=0.0000±0.0004 cm−1 for H–↑C↑–C≡C–C≡C–CH3,D=0.6055±0.0001 cm−1 and E=0.0000±0.0004 cm−1 for H–↑C↑–C≡C–C≡C–C(CH3)3,D=0.5530±0.0002 cm−1 and E=0.0000±0.0006 cm−1 for H–↑C↑–C≡C–C≡C–C6H5,and D=0.8629±0.0003 cm−1 and E=0.0000±0.0010 cm−1 for H–↑C↑–C≡N.The interpretation of the data is based upon the observed spin-density distribution in the alternant free radicals having structures similar to the above triplet molecules. Thus, propargylene, H–↑C↑–C≡C–H, is discussed in terms of a superposition of two π-electron systems having the same spin-density distribution as in the allyl radical. Both positive and negative triplet spin densities are required to account for the observed magnitude of D. The lower values of D obtained for the phenyl-substituted alternant methylenes reflect the delocalization of one of the two triplet electrons into a π orbital of the phenyl group. This effect is more important in the case of phenylpropargylene where a nonzero value of E was obtained. The linear geometry of the alternant methylene chain is responsible for the cases where zero values of E were obtained. The trends in D and trends in linewidths are given qualitative explanations. The discussion assumes that all of the molecules studied have a spectroscopic splitting factor equal to the free-electron value.
Articles you may be interested inPerturbation facilitated optical-optical double resonance spectroscopy of the 23Σ+ g , 33Σ+ g , and 43Σ+ g Rydberg states of 7Li2 A pulsed optical-optical double resonance study of the 11Π g state of 7Li2A study of the E 1Σ+ g state of 7Li2 by pulsed optical-optical double resonance spectroscopy Three Rydberg series of electronic states of 7Li2 have been characterized by pulsed optical-optical double resonance spectroscopy. The observed Rydberg states, which include the previously reported E 'I,+ and G 'n, states, have been identified as 3-1Osu 'I,+,+, In,. The molecular constants for several of the upper members of each of the above series have been used to deduce the ionization potential of 7Li2 and molecular constants for the X 2I,+ state of 7Lit. The former was determined to be T o( 00 ) = 41 496 ± 4 cm -I. The latter were found to be in good agreement with recent ab initio calculations.
An intense laser-induced fluorescence of sodium and of other alkali atoms (K, Rb) at room and lower temperatures has been observed in polysiloxanecoated cells, producing a vapor density of the metal which is much higher than that corresponding to the thermal equilibrium between the vapor and the condensed phase. This enhancement is attributed to the light-induced ejection of atoms absorbed by the polysiloxane coating. The atomic density of the vapor can be manipulated by changing either the laser power or frequency. The dependence of the atomic density on these and other parameters as well as its time-dependent behavior are studied experimentally. A tentative interpretation of the phenomenon is discussed in terms of the properties of solutions of the alkali metals in several solvents.PACS 32.80 -Photon interactions with atoms. PACS 32.80.Fb -Photoionization and photodetachment.
The nuclear magnetic I elaxation times of protons in aqueous solutions of paramagnetic ions have been measured as a function of temperature. For Mn++ ions, the proton TI and T2 were measured at 10 20 and 28 Mc/sec, and for Co++, Cu++, and Gd+++ ions, 20 Mc/sec. The temperature effects observed ca~ b~ explained by incorporating the proper temperature dependences of the several correlation times into the general Bloembergen· Solomon relaxation expressions.In the ~ase of Mn++ solutions, which have a TJ/T2 ratio of about 5.5 at room temperature and 20 Mc/ sec, chemtcal as well as electron exchange and dipolar interactions are found to be important. Analysis of the data by mean? of the e~uations developed pro~ides information concerning the chemical exchange of solvent protons with those m the hydrated Mn++ IOn. An activation energy of 8.4 kcal/mole and other parameters for this process are evaluated.The temperature dependence of TI and Tz in the Co++, Cu++, and Gd+++ solutions can be explained by the temperature dependence of the dipolar interaction alone. Varying the anion in Cu++ solutions had little effect on 1' .1 or its temperature dependence; also, TI for Cu++ solutions was found to vary inversely with concentratIOn over the whole temperature range studied.
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