Molecular beams 242 - INDEX

A brief review of the literature concerning the several materials employed in the fabrication of both TIR and ARROW structures is given in Table 2. The processes employed are completely different, ranging from molecular beam epitaxy to several chemical vapor deposition (CVD) systems, such as low-pressure CVD (LPCVD) or plasma-enhanced CVD (PECVD). As a rule, all suitable materials for ARROWS (and in general for IOCs) should have homogeneous refractive indexes, high mechanical and chemical stability, few... 

The present 1993 edition is a futher revision of the 1988 edition, incorporating the recent resolutions of the CGPM, the new international standards ISO-31, and new recommendations from IUPAP and from other IUPAC Commissions. Major additions have been made to the sections on Quantum Mechanics and Quantum Chemistry, Electromagnetic Radiation, and Chemical Kinetics, in order to include physical quantities used in the rapidly developing fields of quantum chemical computations, laser physics, and molecular beam scattering. New sections have been added on Dimensionless Quantities, and on Abbreviations and Acrohyms used in chemistry, and a full subject index has been added to the previous symbol index. 

Chemisorbed NH3 dissociates much more readily and many authors have studied the kinetics of dissociation. Loffler and Schmidt have studied the kinetics under molecular beam conditions on a polycrystalline specimen and on several low-index faces of a single crystal [(111), (100), (110), (210)]. The rate between 330 and 930 °C is strongly retarded by hydrogen and can be fitted by a Langmuir-Hinshelwood expression with competitive H2 and NH3 adsorption. 

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

Other less definite yet important effects such as profile changes due to nonlinear refractive index alteration in spatially nonuniform high power beams must be carefully considered. As example, the use of nonidentical liquids and optical paths prior to and in, say, EFISH cells and the usual quartz calibration cells could cause potentially inaccurate x determinations. Obviously these types of considerations are important when precise experimentation to test fine models of molecular behavior are intended, but have not stood as obstacle to uncovering the important general trends in molecular nonlinearity enhancement. 

Figure 3.39. Holographic setup for photorefractive molecular glasses. The sample is tilted toward the grating, allowing an applied external field to support the motion of the mobile charges. The phase shift of the refractive index grating can be determined by measuring the transmitted writing beam intensities (two-beam coupling).

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