Collision cross section (CCS) measurements resulting from ion mobility – mass spectrometry (IM-MS) experiments provide a promising orthogonal dimension of structural information in MS based analytical separations. As with any molecular identifier, interlaboratory standardization must precede broad range integration into analytical workflows. In this study we present a reference drift tube ion mobility mass spectrometer (DTIM-MS) where improvements on the measurement accuracy of experimental parameters influencing IM separations provide standardized drift tube, nitrogen CCS values (DTCCSN2) for over 120 unique ion species with the lowest measurement uncertainty to date. The reproducibility of these DTCCSN2 values are evaluated across three additional laboratories on a commercially-available DTIM-MS instrument. The traditional stepped field CCS method performs with a relative standard deviation (RSD) of 0.29% for all ion species across the three additional laboratories. The calibrated single field CCS method, which is compatible with a wide range of chromatographic inlet systems, performs with an average, absolute bias of 0.54% to the standardized stepped field DTCCSN2 values on the reference system. The low RSD and biases observed in this interlaboratory study illustrate the potential of DTIM-MS for providing a molecular identifier for a broad range of discovery based analyses.
The absolute photoabsorption, photoionization and photodissociation cross sections and the photoionization quantum efficiency of ammonia and deuterated ammonia have been measured from the ionization threshold to 25 eV using a double ion chamber and monochromated synchrotron radiation. The photoabsorption spectrum displays extensive vibrational progressions associated with Rydberg series converging onto excited vibrational levels of the 2A2´´ state. New structure has been observed for ND3 in the 10.0-11.3 eV range, and vibrational progressions due to transitions into the , and Rydberg states have been recorded with improved resolution. Features have been observed, for the first time, in the photoabsorption spectra of NH3 and ND3 due to Rydberg series converging onto the à 2E ionization threshold, and interpretations for some of these features have been proposed based upon the corresponding photoelectron spectra. The He I excited NH3+(1a2´´)-1 2A2´´ photoelectron band has been studied experimentally at a resolution of 3 meV and two vibrational progressions, each involving excitation of the 2+ mode, have been observed. The vibrational lines in the main progression show a complex structure associated with rotational excitations. This structure changes gradually in a way that can be explained by the variation of the H-N-H bond angle with the 2+ mode. The effective bond angle has been found to be 120° for v2+ = 0, and similar to that of the neutral ground state near v2+ = 6. The second progression, of weak lines, has been interpreted tentatively as being due to n2++4+. The 4+ mode is doubly degenerate and the excitation of a single quantum has been explained by vibronic coupling with the à 2E state. In addition, He II excitation has been used to record the entire valence shell photoelectron spectrum.
Valence and C1s core level photoelectron spectra of gaseous alanine have been recorded with synchrotron radiation. Using ab initio Green's Function calculations of the vertical outer valence ionization energies and CMS-XR calculations of the orbital ionization cross-sections, it is possible to account well for the features of both the new hν ) 92 eV valence photoelectron spectrum and also its differences with an earlier hν ) 21.2 eV spectrum. Good agreement may be achieved by considering just the contribution of a single molecular conformation. This agrees with previous experimental findings, but conflicts with calculations which suggest that a range of molecular conformations would coexist in an equilibrium sample. A study of the valence photoelectron spectrum of the amino acid threonine complements that of alanine, but unlike the latter is limited by the effects of thermal decomposition of the sample. The C1s core level spectrum of alanine is reported and its peaks are assigned to ionization of the three C atoms in the molecule. A fourth minor peak that is observed is tentatively assigned to a peptide CONH 2 linkage which may be formed between alanine monomers.
Inner-shell photoelectron spectra of the N 1s level in N 2 have been measured with sufficient resolution to resolve the splitting between the gerade and ungerade components. The selective enhancement of the gerade component on the N 2 σ shape resonance is clearly seen, confirming that the resonant behavior is mainly caused by the σ u channel. The splitting of the two components is found to be 97(3) meV.
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