J.D. Morrison

High Efficiency Collision-Induced Dissociation in an RF-Only Quadrupole.

Collision-induced dissociation (CID), when performed in an RF-only quadrupole is a highly efficient method of fragmenting ions. The low-energy (5-10 eV) CID process, may involve direct vibrational excitation by momentum transfer but in any case, is a very different process from the high energy (3-10 keV) electronic excitation CID process observed in MIKES and CAMS. Experimental results are presented which demonstrate the efficiency of CID fragmentation (up to 65%), the elimination of scattering losses, and the effects of varying such experimental parameters as choice and pressure of collision gas, ion velocity in the quadrupole, and quadrupole RF voltage and frequency. The appearance of the CID fragmentation spectra is roughly similar to 14 eV EI spectra. The results of digital simulation of ion trajectories in an RF-only quadrupole are presented. The correspondence between simulated and experimental results aids in the understanding of the quadrupole CID process. The high efficiency of the CID process in an RF-only quadrupole is significant in the development of a tandem quadrupole mass spectrometer for selected ion fragmentation studies.

A mass spectrometer for the study of laser-induced photodissociation of ions

Abstract The design and construction of a tandem quadrupole mass spectrometer for the study of ion photodissociation processes induced by a tunable dye laser is described. A computer-controlled data collection system is employed which allows the resolution of fine structure in photodissociation efficiency curves for ions and permits the detection of excited states of the primary ions.

Ionization and dissociation by electron impact III. CH4 and SiH4

Abstract The electron impact induced ionization and dissociation of CH4 and SiH4 have been studied using a quadrupole mass spectrometer. Deconvoluted first differential ionization efficiency curves are presented and structural features of the parent and fragment ion curves discussed in terms of their contribution to the total differential ionization cross section. A comparison is made with the corresponding photoionization and photoelectron spectra.

The photodissociation of some alkyl iodide cations

Photodissociation of the molecular ions CH3I+, CD3I+, C2H5I+, and n‐C3H7I+ and of the radical ion ⋅CH2I+, has been studied using a tandem quadrupole mass spectrometer and a flashlamp pumped tuneable dye laser. Predissociation of CH3I+ and CD3I+ results in very detailed spectra, which are assigned, and which permit measurement of, vibrational frequencies for the ? states of these ions. The spectra for C2H5I+, n‐C3H7I+, and ⋅CH2I+ consist of broad and structureless bands. In the case of C2H5I+ this is believed to be due to the very short lifetime of a predominating ? state, while in n‐C3H7I+ the dissociation is thought to arise from direct transitions between the two lowest states of the ion which are analogous to the spin–orbit components in CH3I+. In the case of the ⋅CH2I+ radical, the lack of structure is attributed to the formation of the primary ion with a wide spread in internal energies.

A laser‐induced photodissociation study of CH3I+ and CD3I+ at high resolution

Photodissociation of the molecular ions CH3I+ and CD3I+ has been studied at a resolution of better than 0.3 cm−1 (37 μeV) using a triple quadrupole mass spectrometer and flashlamp pumped tunable dye laser. Calibration of the energy scale is achieved by recording the absorption spectrum of iodine vapor simultaneously with the photodissociation spectra. Several spectra are presented, showing partially resolved rotational structure. To assist with a preliminary analysis, deconvolution is used to improve the effective resolution of the data.

Ionization and dissociation by electron impact: I. H2O and H2S

Abstract The electron impact induced ionization and dissociation of H 2 O and H 2 S have been studied using a quadrupole mass spectrometer. Deconvoluted first differential ionization efficiency curves are presented and structural features of the parent and fragment ion curves discussed in terms of their contribution to the total differential ionization cross section. A comparison is made with the corresponding photoionization and photoelectron spectra.

Ionization and dissociation by electron impact II. NH3 and PH3

Abstract The electron impact induced ionization and dissociation of NH 3 and PH 3 have been studied using a quadrupole mass spectrometer. Deconvoluted first differential ionization efficiency curves are presented and structural features of the parent and fragment ion curves discussed in terms of their contribution to the total differential ionization cross section. A comparison is made with the corresponding photoionization and photoelectron spectra.

A combined time averaging—deconvolution technique applied to electron impact ionization efficiency curves

Abstract Using a small digital computer and a quadrupole mass spectrometer, a combined time averaging—deconvolution technique has been developed. Time averaging of first differential ionization efficiency curves produced by electron impact is shown to enhance greatly the signal-to-noise ratio. These data are directly recorded and deconvoluted to nullify the effect of the electron energy spread. Typical results obtained for N 2 + and CO 2 + are discussed.

Interaction Phenomena in Ionization Processes

It is suggested that in several instances, ionization of atoms and molecules by photon and electron impact may exhibit an interaction phenomenon, whereby the lower charged or parent ion cross‐section decreases at the appearance energy of the multiply charged or fragment ion. This competition between cross sections is first interpreted in terms of configuration interaction and then in relation to a collision complex model, similar to the compound nucleus model used to describe nuclear excitation processes.

Laser induced photodissociation of O2

The photodissociation spectrum of O2+, over the energy range 1.7–2.6 eV, has been recorded using tandem quadrupole mass filters and a tunable dye laser. Many of the peaks in the spectrum have been examined at higher resolution and fine structure is observed. A discussion is given of the states involved in the photodissociation. It is believed that processes of both direct dissociation and at least one, but possibly two, types of predissociation are occurring.