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Computational Evaluation of Third-Order Optical Nonlinearities
Published in Hari Singh Nalwa, Seizo Miyata, Nonlinear Optics of Organic Molecules and Polymers, 2020
For second hyperpolarizability, the -???).?component is by far the largest since for the polyazine linear chain, the y component of the transitional dipole moment is much larger than Ihat of x and z components. There is a further increase in the yvvvv value with the increased chain length because of the larger number of contributing terms. The magnitude of the transitional moments along the chain axis increases steadily with chain length, since longer chains have a large transitional moments, therefore, larger ????,. values are obtained. The oligomeric polyazine derivatives, having repeat units 1, 2, 3, 4, and 5, exhibit orientationally averaged (y) values of 3.34 X !0 36. 1.97 X IO :\ 5.71 X 10". 1.12 X IO11. and 1.75 X 10 " esu, respectively, indicating an order of magnitude increase from the monomer to the trimer polyazine derivative. Figure 8 shows the log-log plot of ?????values vs. the number of nitrogen and carbon atomic sites for a well-defined conjugation length polyazine chain. The yvalues increase much more rapidly as the ? electron delocalization length of polyazine backbone increases; its value changes by a factor of 6 in going from the monomer to the dimer and by a factor of 17 in going from the monomer to the trimer. The yvalue increases by a factor of more than 53 from the monomer to the pentamer polyazine derivative. Like other conjugated systems, a significant increase in yvalues is observed for polyazines. The increase of ynyy obeys A3"2 power law for 3 repeat units (A = 3), then
Characteristics of Polymers and Polymerization Processes
Published in Manas Chanda, Plastics Technology Handbook, 2017
Step polymerization occurs by stepwise reaction between functional groups of reactants. The reaction leads successively from monomer to dimer, trimer, tetramer, pentamer, and so on, until finally a polymer molecule with large DP is formed. Note, however, that reactions occur at random between the intermediates (e.g., dimers, trimers, etc.) and the monomer as well as among the intermediates themselves. In other words, reactions of both types, namely, n-mer+monomer→(n+1)-mer and n-mer+m-mer→(n+m)-mer occur equally. Thus, at any stage the product consists of molecules of varying sizes, giving a range of molecular weights. The average molecular weight builds up slowly in the step polymerization process, and a high-molecular-weight product is formed only after a sufficiently long reaction time when the conversion is more than 98% (see Figure 1.18a).
The Structure of Water
Published in Tadahiro Ohmi, Ultraclean Technology Handbook, 2017
The water we actually use has 1023 molecules. The assumed number of molecules—1000—is rather small compared with the actual figure, but it is close to the limit of the processing capability of conventional computers. In this sense, a discussion based on the molecule number of 1000 should be at the highest level. The reliability of the pentamer- monomer model is considered very high.
Structured water chains in external electric fields
Published in Molecular Physics, 2020
Smita Rai, Nayan Sharma, Dhurba Rai
The overall evolutionary trends of the HOMO–LUMO energy gap (cf. Figure 7) and the average binding energy (cf. Figure 6) with electric field show that there is no strong correlation between the chemical and energetic stabilities of the clusters under consideration. The HOMO–LUMO energy gap decreases after reaching a maximum at the threshold field, while the average binding energy increases monotonically. However, a closer look reveals an inverse correlation between the average dipole moment per monomer and the electronic property, i.e. the HOMO–LUMO energy gap. Each unit of pentamer chain clusters under consideration has the lowest average dipole moment per water monomer (cf. Figure 5) while the threshold field is highest (cf. Figure 8), followed by that for the tetramer and hexamer clusters. This suggests that the pentamer chains are the most favourable water clusters over others, thereby further confirming the experimental observation of nucleation of water pentagon chains on the Cu substrate [94].
Precision characterization of three ultrafine condensation particle counters using singly charged salt clusters in the 1–4 nm size range generated by a bipolar electrospray source
Published in Aerosol Science and Technology, 2020
Sophia Brilke, Julian Resch, Markus Leiminger, Gerhard Steiner, Christian Tauber, Peter J. Wlasits, Paul M. Winkler
When classifying the monomer, dimer and trimer, we observe peaks of clusters of with acetonitrile and ethanol. Ethanol is used for rinsing the capillaries before and after each measurement run. Though RH in the system is monitored and kept to a minimum (<3.5% RH), we also detect water clusters. In the case of the classified monomer, an additional prominent peak is observed at m/z = 232 Th which was not identified here. The relative abundance of this peak to the expected monomer peak at m/z = 79 Th is 0.2:1. This peak might originate from forming adducts with possible impurities in the pressurized air used as carrier gas. At larger clusters, an additional signal at a similar distance to the cluster mass of the classified mobility peak is noted. For classified clusters up to n = 4 (pentamer), a monomer peak is detected with highest relative abundance for the classified trimer (5:1). As discussed earlier, we suggest that the smaller clusters originate from evaporation at the TOF transition which was also suggested by previous tandem DMA-MS studies (Ude and Fernández de la Mora 2005). At larger clusters (n > 3), an additional ion signal in the region of the classified cluster is recorded. Due to the low resolution in this high mass range, these peaks cannot be identified. Since the operational settings are at the experimental limit of the instrument, we cannot exclude that the signal originates from scattering of heavy ions, i.e., the large clusters, at the detector.