Articles you may be interested inMolecular near-field antenna effect in resonance hyper-Raman scattering: Intermolecular vibronic intensity borrowing of solvent from solute through dipole-dipole and dipole-quadrupole interactions Electron spin relaxation of ditertiarybutyl nitroxide in supercooled water New measurements of the solvent effect on the nitrogen hyperfine coupling constant of di-tert-butyl nitroxide are reported. These, together with literature data, are used to test various models for the solvent effect. At the Huckel level of approximation, aN is a linear function of the applied electric field. Thus various reaction field theories may be considered. The widely used Onsager reaction field does not account for the effects of the more polar solvents or for the differences between polar and nonpolar solvents. The Wertheim and Block-Walker reaction fields are better, especially for very polar solvents. However none of these continuum reaction fields is entirely satisfactory theoretically or experimentally. We propose a dipole-dipole model for polar solvents which is superior to the continuum models. From the dipole-dipole model, we suggest that the quantity IJp/M is a convenient linear parameter for polar solvent effects, the factors being solvent dipole moment, density, and molecular weight. The dipole-dipole model should apply to a wide range of polar solutes. Some special situations are not explained by the model, including hydrogen-bonding solvents, halogenated aromatiCS, and solvents with more than one conformation. The temperature dependence of the solvent effect is also considered.

Region to the south. Four other species are predominantly inhabitants of the Deciduous Forest Region Affinities Ten native Ottawa District species, most with and they are near or at their northern limits here: northern affinities, also occur in Europe and/or Asia Aplectrum hyemale, Galearis spectabilis, as the same or a different variety: Calypso hulbosa. Platanthera flava var. herbiola and Spiranthes cerifidn iia. The distributions of four species, Calopogon repens, Liparis loeselii, Listera cordata, Malaxis tuberosus, Corallorhiza rnaciilata, C striata and monophylla, Platanthera hyperborea, P. obtusata Malaxis unifolia, reach various parts of Mexico, and Spiranthes rotnanzoffiana (Luer 1975). In addi-Central America and the West Indies (Luer 1975; tion, Epipactis helleborine is a relatively recent Homoya 1993). arrival 12 41 85 13 16 The Canadian Field-Naturalist Vol.111 Capsules and Seeds Capsules autogamous (Catling and Catling 1991), regularly Capsules of some Ottawa District orchids collect-approach 100% yields. A third group of species ed after seed release are illustrated in Figures lad.tends to have rather random yields but with an These species were chosen to complement those appreciable number of plants approaching 100%shown by Homoya (1993) for Indiana, which are yields. This group includes Coeloglossum viride, also representative of plants in the District except for Epipactis helleborine, Platanthera clavellata and Spiranthes lacera. The specimen of Platanthera P. hyperborea, all of which are reported to be autohyperborea illustrated by Homoya is comparable to gamous (Catling 1983a; Catling and Catling 1991), the mesic forest plant of the Ottawa District. Sizesat least in some parts of their ranges. Corallorhiza maculata and Spiranthes lacera usually have Among species, the smallest capsules are those of yi^^ds over 50%, the first of these also being Listera cordata at 0.3 x 0.2 cm and the largest are reported as being autogamous (Catling 1983a; \ho?,e oi Cypripedium reginae dii?>.(y x 1.2 cm. Catling and Catling 1991). Goodyera pubescensThe Canadian Field-Naturalist Vol, 1 1 1 Methodology The species descriptions are based on our observaseeds. These characters were chosen because they tions made in the field in the Ottawa District and the allowed a more quantitative account or were othersurrounding Study Area since 1966 and on herbari-wise of interest to us. Other aspects are well covered um specimens from the same areas examined at the by recent publications (for example: Smith 1993; following institutions (listed in Index Herbariorum Homoya 1993). Part I (Eighth Edition)): Canadian Museum of Nature (CAN), Carleton University (CCO), Heights: The heights are based on our measure-Agriculture Canada (DAO), Field Museum of ^"'1,^^h erbarium specimens and plants in the Natural History (F), Royal Botanical Gardens ^'^^tl range is reported along with the range (HAM), Universite de Montreal (MT), McGill University (MTMG), U.S. National Arboretum including one standard deviation about the mean. See Num...

TABLE VIII: Band Assignments for the Species Produced in the Matrix Reactions of In and Ga with 16G2 frequency,0,6 cm"1 assignment6 In + 1 02 Ga + ,602 species mode 1084.2 1089.5 \ ( l'i(Ai) 332.2 380.0 > mo2(c2U) WA,). [277.7] 285.5 ) U(B.) 1015.9(N2) 1015.6(N2) 02M-M02(D2d) ,s(B2), 0-0 443.2(N2) 458.6(N2) M02M(D2h) M / \ Vs(B2u) [816.2] M-d zO[C2U] M M / \ MA.) 554 795.3(N2) 968.0 952.7(N2)<'(BU) 0 Values are for Ar matrices unless specified otherwise. 6 Tentative assignments are indicated by brackets.

The preparation of crystalline pyrene, perylene, and azulene perchlorates is reported. Details of the novel method, growth on the anode in an electrolytic cell, are given. Crystalline samples of each compound give EPR resonances with very narrow linewidths, about 0.1 G. The resonances from the pyrene and perylene salts each consist of two components. One follows a Curie law and dominates at low temperature. It is attributed to “impurities,” probably lattice defects. The other component, dominating at high temperature, arises from thermally generated Wannier triplet excitons. The excitation energies are 0.18 and 0.27 eV for the pyrene and perylene salts, respectively. The azulene salt yielded only the “impurity” signal within the available temperature range.

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