Double-reflection spectrum measurement

It should be noted that the experimental spectra are not corrected for double passage of light through the sample. Losses of light to double reflection and absorption of dye film must be considered in order to obtain the true value of the optical density in our optical setup. For this, the reflectance spectrum of J-aggregated PIC 2-18 film was measured (Fig. 25). The corrected optical density of J-aggregated film D(Xcor)=log [Io/(fo--A-R)] was calculated by solving the quadratic equation for the absorption coefficient obtained from the formula for the measured optical density D(A) ... 

The reflectance / of a dielectric material (nonmetallic material) is generally low. In particular, reflectance for a double-reflection measurement is often much smaller than unity. This makes the quality of the resultant infrared spectrum unsatisfactory. Even in a singlereflection measurement, the situation is similar if the refleetance from the sample is low. 

Reference and sample measurements are performed consecutively, and the resultant (sample) spectrum is obtained as the ratio of the two photon fluxes onto the detector. In a single-beam spectrometer, there are no other options in a double-beam spectrometer, the photon fluxes of the sample and reference beam path are compared. When an integrating sphere is used with two ports and a white standard in the reference position, the photon fluxes are comparable to each other, and no problems occur. Note that the ports are part of the sphere and that any material change in the reference or sample position will change the average sphere reflectance pave. The reference measurement should be conducted with exactly the same components (windows) as the sample measurement otherwise, "substitution errors" may occur. 

The absorption spectrum studies presented above merely reflect the electronic environment of the molecule and do not give specific information about the type of interaction. The data which must be accounted for in considering a physical mode for the binding process can be derived from several different approaches. Hydro-dynamic measurements on the DNA-drug complex are of interest, since Lerman58, S9 has established that an increase in the intrinsic viscosity of DNA and a decrease in the sedimentation coefficient of the polymer are two criteria for intercalation of ring systems between base pairs of a double-helical DNA. 

In spectroscopic investigations, the quantities of interest are the transmission or reflection of the sample. In order to obtain these, the background spectrum (without sample in the spectrometer) and the sample spectrum have to be measured (Fig. 9), and their ratio calculated. In commercial double-beam instruments, this ratio is obtained automatically. 

The electrochemical behaviour of stainless steel has not been worked out completely, although the measured data are available. However, one aspect of the behaviour, based on the measured double layer capacity data, seems to be susceptible to interpretation. The capacity-potential curves are determined by the state of the metal surface and by the ionic environment. In this work, it has been assumed that the ionic environment is a constant. This means that the double layer capacity-potential curves should reflect the nature of the metal surface just as, say, an electron energy spectrum in surface science. Stainless steel has a complicated electrochemical behaviour. In previous work [22] an attempt has been made to compare the double layer capacity curves measured during dissolution and passivation of the stainless steel with that of the pure components. It seems that all the data in the high frequency regime can be fitted to eqn. (70) with the Warburg coefficient set equal to zero. 

Figure 18 shows IR-UV depletion spectra of [GS + 2H] measured by fixing the UV laser wavenumber to transitions assigned to conformers A, B, and C in the spectrum of Fig. 17a. Each IR spectrum reflects the specific vibrational frequencies associated with the different conformers giving rise to the probed UV transitions. Several IR bands in the spectrum of conformer A appear to be doubly degenerate. For example, the five peaks lying between 1,600 and 1,700 cm belong to the ten bands that have primarily C=0 stretch character. This double degeneracy implies that pairs of oscillators are situated in equivalent positions in the molecule, and since GS is cyclic, this conformer must have C2 symmetry [158].

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