Effect of supporting modes

As already discussed in Section 13.1, the multiphonon pathway for vibrational relaxation is a relatively slow relaxation process, and, particularly at low temperatures the system will use other relaxation routes where accessible. Polyatomic molecules take advantage of the existence of relatively small frequency differences, and relax by subsequent medium assisted vibrational energy transfer between molecular modes. Small molecules often find other pathways as demonstrated in Section 13.1 for the relaxation ofthe CN radical. When the concentration of impurity molecules is not too low, intermolecular energy transfer often competes successfully with local multiphonon relaxation. For example, when a population of CO molecules in low temperature rare gas matrices is excited to the v = 1 level, the system takes advantage ofthe molecular anhannomcity by undergoing an intermediate relaxation of the type 

As another interesting example consider vibrational relaxation of an HCl molecules embedded in an Argon matrix. At T = 9 K it is found that transition rates between the lowest vibrational levels are = 8 x 10 s (ct = 2871 cm ) and A l 2 = 3.8 x 10 s (to = 2768 cm ). These transitions are resolved because of the molecular anharmonicity, and the fact that A 1 2 seems to agree with expectations based on the energy gap law. On the other 

Dubost in Chemistry and Physics of Matrix Isolated Species, edited by L. Andrews and M. Moscovits (Elsevier, Amsterdam, 1989). 

Here the subscript 1 denotes the local mode and the other modes are represented by the Einstein frequency of the order of the solvent Debye frequency, and we have assumed that a i a 2. 

In this case the temperature dependence is expected to be much weaker than before, Eq. (13.66), because the temperature dependent factor (/ta+l) is raised to a much smaller power. Moreover, the larger is thefrequency ofthe local phonon the smaller is I, therefore, since oti C 1, the larger is the rate. 

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The nutrient sparing effect of antibiotics may result from reduction or elimination of bacteria competing for consumed and available nutrients. It is also recognized that certain bacteria synthesize vitamins (qv), amino acids (qv), or proteins that may be utilized by the host animal. Support of this mode of action is found in the observed nutritional interactions with subtherapeutic use of antibiotics in animal feeds. Protein concentration and digestibiHty, and amino acid composition of consumed proteins may all influence the magnitude of response to feeding antibiotics. Positive effects appear to be largest... 

Careful attention to quantitative activity vs. concentration relationships, to the effect of interaction terms in combinations (using computerized regression analysis and experimental design), and careful observation of the manner in which one mode of action supports and reinforces another, seems likely to lead us to the next generation of highly efficient flame retardant systems. 

Methods for Reducing Toxic Effects. All of the treatment methods currently available for use in di-n-octylphthalate ingestion or skin contact are supportive in nature and/or involve decreasing the absorption or increasing the rate of elimination of di-n-octylphthalate (Stutz and Ulin 1992). Since the mechanism of di-n-octylphthalate toxicity is not known, there are currently no methods that focus on mitigating the effects of di-ft-octylphthalate by interfering with its mode of action. Therefore, more information on the mechanism of action for di -/ -octy lphthalate is needed in order to devise methods for the mitigation of its toxic effects. 

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