ALBERT

Notes: Using our exact finite temperature time-correlator model expressions for the optical absorption and resonance Raman (RR) excitation profiles including full linear plus quadratic electron–phonon coupling and linear non-Condon coupling, we have generalized the absorption→RR profile transform technique to normal modes that have both mode mixing (Dushinsky rotation) and linear non-Condon coupling. The new approximate transform provides a useful and convenient method for extracting information on mode mixing from measured RR excitation profiles. Compared with full model calculations, which are often prohibitively difficult for complex multimode systems owing to the fact that values of all of the model parameters are needed, the new transform is advantageous. This is because it allows one to compute a mode's finite temperature profile using just the measured finite temperature absorption and model parameters of only the Raman mode plus those modes directly mixed with it. The information about the remaining modes is carried through the calculation via the use of the measured absorption. Numerical illustrations will be presented on the use of the new transform as a probe of mode mixing. Comparison with a previous transform relation which includes only mode mixing and is restricted to T=0 K will also be discussed.

Notes: Finite temperature model expressions for the excitation profiles of second-order Stokes resonance Raman (RR) scattering are derived within the framework of the time correlator theory for systems with simultaneous linear electron–phonon coupling and linear non-Condon coupling. These expressions have all the advantages common to solutions from the time correlator theory, allowing convenient and efficient multimode modeling procedures. These results, together with those obtained elsewhere for the second-order profiles of systems within the Condon approximation, but having mode mixing and frequency shifts, are applied to the RR scattering originating from the 700 nm absorption band of azulene. For this system, it was shown previously that the measured optical absorption and fundamental RR profiles cannot discriminate between a mode mixing model, invoked to account for the measured relative intensities of the fundamental profiles of two modes, and an equally successful non-Condon model; nor can recent quantum-chemistry calculations by others for this system. With our new model expressions for the second-order profiles, we calculate here the profiles of the combination/overtone bands involving these two modes, using either the same mode mixing model parameters, or the same non-Condon model parameters which were previously successful for the absorption and fundamental profiles. Our results show that the second-order profiles predict a clear discrimination between the two models.

Notes: Resonance Raman (RR) profiles of the 1005, 1155, and 1525 cm−1 modes of β-carotene dissolved in carbon disulfide have been measured at room temperature and at 172 K. Previous studies, based upon room temperature measurements, have indicated that inhomogeneous (i.e., site) broadening may be important for this system. Our measurements are the first RR data for this system at two temperatures. Such data are necessary in order to study the relative importance of inhomogeneous broadening and thermal broadening. Using previously developed transform techniques, we analyze our RR data by calculating profile line shapes directly from our measured optical absorption data for each temperature. The assumptions underlying this analysis do not include inhomogeneous broadening, and the calculations yield profile line shapes which are in quite good overall agreement with the measured profile line shapes for all three modes at both temperatures. We have also extended the transform calculations in order to incorporate inhomogeneous broadening. However, the agreement between the measured and calculated RR profile line shapes is not substantially improved by the inclusion of inhomogeneous broadening in the transform analysis.

Notes: In a recent paper (Az I), well-structured T=300 K resonance Raman (RR) profiles for the 1400, 1260, 900, and 2×825 cm−1 lines of azulene in CS2 and for the 825 cm−1 line of azulene in methanol were reported. Previously developed transform techniques were used to (1) compute RR profile line shapes directly from measured optical absorption spectra, and (2) extract ratios of Stokes loss parameters from the line shape scale factors. The transform analysis indicated that (1) our model assumptions (adiabatic and Condon approximations, harmonic phonons, atomic equilibrium position shifts, and small vibrational frequency shifts upon excitation to a single electronic state) are basically correct allowing forminor modifications, and (2) any deviations from these assumptions are likely to be larger for the 900 cm−1 mode and smaller for the 1400 and 1260 cm−1 modes. In this paper (Az II), we report model calculations of the optical absorption spectra, RR profile line shapes, and relative RR intensities. In these calculations, we use a recently proposed nonzero temperature multimode time-correlator modeling procedure. Compared with the conventional sum-over-states method, our time-correlator modeling procedure is superior in that (1) our optical absorption spectra and RR profiles computed via fast Fourier transform techniques have a practically unlimited spectral range and (2) the computing times are short for nonzero temperature multimode calculations. In our basic model, we adopt the assumptions of Az I and use seven azulene modes to obtain simultaneous good fits of the well-structured RR profile line shapes and optical absorption spectra. However, we find that the basic model does not account for the intensity of the 900 cm−1 Raman line relative to that of the 1400 cm−1 line, even though the individual profile line shape fits for these modes are very good. The basic model is therefore modified to allow mixing of the normal coordinates of these two modes. By introducing a single, relatively small mode-mixing parameter, we obtain a good fit of the relative RR intensities in addition to simultaneous detailed fits of the optical absorption spectra and RR profile line shapes. In an alternate approach, we modify our basic model and find that the inclusion of two relatively small non-Condon parameters, instead of one mode mixing parameter, can also produce simultaneous detailed fits of all of our optical absorption and RR data.A comparison of the two modified models solely on the basis of simplicity favors the mode-mixing model, since only one extra parameter is required to modify our basic model.

Notes: Summary. Information on the use of herbicides in the 1959-60 crop year was collected from a stratified random sample of farms in each of four arable farming districts in Eastern England.In each of the surveyed districts about 80% or more of the area under cereals, 10-20% of other tillage crops and about 10% of the grassland was treated with herbicides. In the three diatricts where peas were widely grown most of this crop was also treated. Contract services were used most on the smaller farms.MCPA was the most widely used herbicide on cereals, but in two of the four districts mecoprop was also often used. Manufacturer's reeommendations for rates of application were followed fairly closely for MCPA on cereal crops which were not undersown but MCPA was also used on much of the undersown cereals in spite of the risk of damage to the legumes. MCPB and mecoprop were often applied to cereals at rather lower rates than those generally recommended, Little detailed information was obtained about when herbicides were applied but clearly most farmers were influenced more by general crop appearance (and possibly date) than by the stage of growth of crop or weeds.The weeds most often mentioned by farmers as occurring on areas treated with herbicide were Cirsium spp., Sinapis arvensis. Galium aparine, Stellaria media, Chenopodium album and Rumex spp. The weeds which were most frequently difficult to control were Avena spp.Polygonum persicaria, Tussilago farfara, Stellaria media and Matricaria maritima ssp. inodora. The herbicides used were usually appropriate for the weeds which they were intended to control and nine out of every ten farmers asked were satistified with the results of treatment; it was very rare for any detrimental effect on crops to have been noted.L'emploi d'herbicides dans quatre régions agricoles de l'est de l'Angleterre 1959-60

Notes: In trials carried out in 1978–80, blackgrass populations in winter wheat growing on heavy soil were substantially reduced by all chemical treatments tested, the least effective being methabenzthiazuron. Wild oat populations were also reduced by all treatments except chlofop-isobutyl and methabenzthiazuron. On average of the 3 years only metoxuron treatment gave wheat yields significantly higher than the unsprayed crop.