Optical constants experimental determination

The vibrational spectrum of benzene around 1000 cnf has also been measured. IQ. Benzene was physisorbed on a cooled copper substrate in the vacuum chamber. Figure 19 shows the transmission for several thicknesses of benzene and a prism separation of 3 cm. The thickness was determined from the measured transmission in transparent regions using Eg. (7). The solid curves were calculated from Eqs. (5) and (6) using optical constants for benzene obtained from an ordinary transmission experiment.il The benzene film was assumed to be isotropic. Of the two absorption lines seen, one belongs to an in-plane vibrational mode, and one to an out-of-plane vibration. Since the electric field of the SEW is primarily perpendicular to the surface, the benzene molecules are clearly not all parallel or all perpendicular to the copper surface. Also it should be noted that the frequencies are the same (within the experimental resolution) as those of solid benzene22 and of nearly the same width. These features indicate that the benzene interacts only weakly with the copper surface, as would be expected for physisorbed molecules. 

R = K exp (Q/T), where the constant K incorporates spectroscopic and optical system constants. The value of K was experimentally determined by calibration against a premixed laminar flame with a known temperature produced on a porous plug burner. The characteristic vibrational temperature Q = hcco/k = 3374°K for nitrogen. Here, h is Planck s constant, c is the speed of light, 0) is the vibrational constant, k is Boltzmann s constant, and T is the temperature in Kelvin. 

From the data reported in Fig. 2.2 and from spectroscopic ellipsometry measurements, the anisotropic complex optical constants of oriented PPV have been determined [32,69]. Several different data analyses, described previously, were carried out on the 7Z and T spectra in order to extract n, both below and above the HOMO-LUMO transition (transparent free-standing film and bulk material, respectively). In order to evaluate n below 1.6 eV, where the sum of 1Z and T is equal to 1 within experimental error, a numerical inversion of the 7Z and T spectra was performed by assuming k = 0... 

As everyone knows, the optical properties of a material are expressed in two optical constants, the refractive index n and the absorption coefficient x. It is the purpose of spectroscopy to determine experimentally one or both of these optical constants as a function of frequency. This can be done by measuring reflection or transmission. If we were able to measure amplitudes or electrical fields (magnitude and phase) in an optical investigation, it would generally be possible to deduce both optical constants from one measurement of either reflection or transmission. However, we are only able to measure intensities where the magnitude of the field is determined and the phase information is lost. Thus, in general, from one item of information only one optical constant is obtained, and two measurements are necessary to determine both. There are a few exceptions to this rule, e.g. the... 

But the amplitude or as5unmetric Fourier spectroscopy has not been applied only to solids but also to liquid samples and gases. Here too, it has been proved an important help to obtain the two optical constants n and x simultaneously 62a,b) In gases, for example, the anomalous dispersion of the refractive index in the neighbourhood of rotational absorption lines was determined experimentally by this method. 

The NO2 dissociation rate was measured by a two-color picosecond pump-probe method in which the product NO was monitored by LIF. Of particular significance in this study is that the NO2 density of states at the dissociation limit of 25,130.6 cm is relatively well established from an extrapolation of experimentally determined densities at an energy of 18,500 cm . This density (for cold samples where the rotations do not contribute significant densities) is 0.3 states per cm , (Miyawaki et al., 1993) which leads to a minimum rate constant l/h p( ) = 1 x 10 sec . The experimentally measured rate increases from 0 to 1.6 x 10 sec at the dissociation limit. It is interesting that the subpicosecond laser pulses with their transform limited resolution of about 20 cm do not excite individual NO2 resonance states (see section 8.3, p. 284) but, instead, prepare a superposition of those states that are optically accessible within the laser bandwidth. It is thought that all resonance states in this bandwidth are... 

Figure 7.28 lists all the rate constants in zero field and in an applied magnetic field which must be experimentally determined in order to have a complete understanding of the dynamics of the triplet state and therefore a quantitative understanding of optical spin polarisation the individual population rates Sj (u = x,y,z)... 

Below, we describe a procedure, adapted from the work of AUara et al. [42], which allows one to determine optical constants of a given compound in a solution. A thin-layer transmission optical cell, shown in Fig. 9.13 A, is employed to obtain the experimental data. Two ZnSe or, better, Bap2 discs are used as windows, and a 10- or 25-pm thick Teflon gasket is used as a spacer. The cell is placed in a Teflon housing, clamped between two aluminum plates, and mounted inside the main compartment of an FTIR spectrometer. Teflon tubing is used to fill the cell with fluid samples. Two samples are necessary to acquire a set of experimental spectra needed for calculations the pure solvent is used as a background sample and a solution of a given compound is used as the analyte sample. 

DETERMINATION OF OPTICAL CONSTANTS OF ISOTROPIC ULTRATHIN FILMS EXPERIMENTAL ERRORS IN REFLECTIVITY MEASUREMENTS... 

The theoretical expression for the absorption coefficient in this energy region is given by Eqs. (1), (2) and (4), and hence Bto = A f g. The constant Ag can be evaluated from known materials parameters. Thus we can obtain a value for fq-g (=Bq g/Ag ). Using this value, the expression for the oscillator strength listed in Table I and the experimentally determined ratio K o = 1.0 we compute U g and V-pg individually. From these values, the expressions for yTg and Vq-g from Eqs. (23), optical matrix elements (obtained from k " calculations), energy denominators obtained from the optical transitions and known phonon frequencies we find ... 

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