Stark tuning experiments

On the whole, theoretical results given in Tables 3 and 4 appear to compare more favorably with experiment for smaller clusters than for larger ones. However, due to the above considerations, this cannot be but fortuitous, and the actual predictions of our present calculations are those given with the largest clusters considered in the present study, i.e. PdgCO for on-top and PdioCO for bridge chemisorption, respectively. As far as quantum mechanical calculations of the Stark-Tuning effect are concerned, this result is new, and has probably been underconsidered until now. 

Laser-microwave spectroscopy based on nonlinear phenomena developed from the type of experiments on molecules already discussed in Section 3.2 which make use of optical pumping or double resonance. Occasionally, the laser and the rf power were high enough to create the nonlinear phenomena mentioned above, i.e., to saturate the transitions involved and/or to induce multiphoton transitions. The intermediate level in, e.g., two-photon transitions did not have to be a real state but could be virtual as well. Therefore, a drawback often encountered in earlier infared laser-microwave experiments could be avoided if the laser transition frequency did not exactly coincide with the molecular absorption line the Stark or Zeeman effect had to be used for tuning. This results in an undesired line splitting. With laser-microwave multiphoton processes, however, the laser can be operated at its inherent transition frequency. Exact resonance with molecular lines is then achieved by using a nonlinear effect, i.e., a radiofrequency quantum is added to or subtracted from the laser frequency (see Figure 28). 

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