Peter W. Tiedemann

Dynamics of ion coupling in an FTMS ion trap and resulting effects on mass spectra, including isotope ratios

Abstract We have studied the coupled cyclotron motions of ions at moderate to high density in the ion trap of a Fourier transform mass spectrometer. For the case of two ionic species of similar mass in the ion trap (CO + and N + 2 ) we present image current detection results over a range of ion densities. At low ion densities the ion motions are independent, resulting in two distinct image current frequencies. At higher ion densities the ion motions are strongly coupled. In the high density limit only one of the coupled motions has the symmetry required to generate an image current. Thus, the FT mass spectrum of the CO/N 2 mixture at high density consists of only a single peak at the frequency of the image current active, coupled cyclotron motion. By analyzing the image current transients in detail we can follow the development of the collective normal modes of the ions in the trap. FTMS spectra of naphthalene (C 10 H 8 ) as a function of ion density demonstrate that the coupled ion motions can have a substantial effect on the measurement of 12 C/ 13C isotope ratios.

Formation of XeCl− in the gas phase

Abstract Ion cyclotron resonance has been used to detect the formation of XeCl − at pressure 10 −4 torr from the ion-molecule reaction of COCl − and Xe. The dissociation energy of XeCl − into Xe and Cl − is estimated to be less than 10 kcal/mole. The results suggest that other negative ions similar to XeCl − may be detected by mass spectrometric techniques.

Gas phase proton affinities of carbonyl compounds by ion cyclotron resonance spectroscopy

Pressure studies and the double resonance technique of ion cyclotron resonance spectroscopy have been used to establish the following orders of proton affinities for carbonyl compounds in the gas phase: HCOOH < HCOOCH3 < CH3COOH < HCOOC2H5 < CH3COOCH3≈ CH3COCH3 < CH3COOC2H5; CH3COCH3 < CH3COC2H5 < C2H5COC2H5. The order of proton affinities in these compounds is shown to follow the decrease in ionisation potential of homologous compounds and the inductive effect of alkyl substituents. An ester and its corresponding thioester have been found to have approximately equal proton affinity.

Eletrodo de hidrogênio: o que há nos livros didáticos além de E¸ = 0?

The results of an exercise on electrochemistry for General Chemistry students are presented. The difficulty encountered by students in predicting the shift in the potential of the hydrogen electrode under non-standard conditions prompted a search in textbooks on how the subject is developed. Besides several instances of inconsistencies in defining the standard state, such as including the temperature in the definition, a number of incorrect depictions of the hydrogen electrode were discovered. Of the 28 General Chemistry books, 16 Physical Chemistry books and 24 Internet pages, 30, 20 and 46%, respectively, showed devices that would not work in practice.