Nitrogen ions molecular calculations

Several instniments have been developed for measuring kinetics at temperatures below that of liquid nitrogen [81]. Liquid helium cooled drift tubes and ion traps have been employed, but this apparatus is of limited use since most gases freeze at temperatures below about 80 K. Molecules can be maintained in the gas phase at low temperatures in a free jet expansion. The CRESU apparatus (acronym for the French translation of reaction kinetics at supersonic conditions) uses a Laval nozzle expansion to obtain temperatures of 8-160 K. The merged ion beam and molecular beam apparatus are described above. These teclmiques have provided important infonnation on reactions pertinent to interstellar-cloud chemistry as well as the temperature dependence of reactions in a regime not otherwise accessible. In particular, infonnation on ion-molecule collision rates as a ftmction of temperature has proven valuable m refining theoretical calculations. 

Example the molecular ions of nitrogen, N2, carbon monoxide, CO, and ethene, C2H4, have the same nominal mass of 28 u, i.e., they are so-called iso-baric ions. The isotopic masses of the most abundant isotopes of hydrogen, carbon, nitrogen and oxygen are 1.007825 u, 12.000000 u, 14.003070 u and 15.994915 u, respectively. Using these values, the calculated ionic masses are 28.00559 u for Nz"" , 27.99437 u for CQ-", and 28.03075 u for CjH/. This means they differ by some millimass units" (mmu) from each other, and none of these isobaric ions has precisely 28.00000 u (Chap. 3.3.4 and Chap. 6.9.6). 

Molecular orbital methods have been applied with increasing success to the calculation of the UV spectra of the quinolizinium ion (71MI21000) and have been extended to the three benzoquinolizinium ions as well as to some tetracyclic systems having an azonia nitrogen (70G421). 

Nitrogen (as 15N) and oxygen (as 170) also contribute to (M + 1)+, if present, while wO and two 13C s contribute to (M + 2)+. The calculated intensities of (M + If- and (M + 2)+ relative to M+ (as 100) are tabulated in Table 9-5 for elemental composition of ions up to C20. The table applies to fragment ions as well as molecular ions, but the intensity data from fragment ions very often is complicated by overlapping peaks. 

In a first step, intermediate species form rapidly upon mixing the lanthanide ion with EUdota. Both excited state luminescence lifetime determinations for the Eum complex (Chang et al., 2001) and molecular mechanics calculations are consistent with a structure in which the lanthanide ion is coordinated to four carboxylate groups, well away from the nitrogen atoms of the macrocycle, two of which are protonated. This intermediate may react with a hydroxide group to form monoprotonated neutral species in a rapid equilibrium. 

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