M. F. Steuer

Dissociative ionization of N/sub 2/ produced by 1-MeV H/sup +/ and He/sup +/: Time-energy spectroscopy

By measuring the energy and time of flight of fragment ions from molecular breakup, the fragments can be separated according to their mass to charge ratios, and the kinetic-energy spectra for each, recorded. This technique is applied to the dissociative ionization of N/sub 2/ caused by 1-MeV H/sup +/ and He/sup +/ projectiles. The energy spectra for N/sup +/ is not unlike that produced by electron bombardment, but the N/sup + +/ spectra show some high-energy structure that has not been previously observed. An N/sup 3 +/ spectrum is obtained with a maximum near 25 eV, and the reflection method is used to obtain a potential curve for a presumed N/sub 2/ /sup 3 +/ state. (AIP)

Dissociation of CH4 by 1 MeV H+, He+, and O+ projectiles

Methane is bombarded by 1 MeV H+, He+, and O+ projectiles. Kinetic‐energy spectra are presented for fragment ions with integer mass‐to‐charge ratios of 1,2,3,4,6, and 12. The H+ and H+2 kinetic‐energy spectra show well‐defined structure which is indicative of two‐body breakup of the CH4. In addition, the H+ spectra exhibit high‐energy tails which may be attributed to multibody breakup. This feature is greatly enhanced in the H+ energy distribution produced with O+ projectiles. Bombardment with O+ projectiles also produces carbon fragments Cq+(q=1,2,3), C4, and/or H+3.

Dissociation of CO2+2 ions into CO+ and O+ fragments

Dissociative ionization of CO2 is further studied by the bombardment of 1‐MeV He+ ions. The coincident detection of CO+ and O+ fragment pairs confirms the dissociative channel CO22+→CO++O++6.0 eV which is the principal contributor to the ion yield. (AIP)

Dissociation of CH3Cl by 1 MeV H+, He+, and O+

The dissociation of methyl chloride produced by bombardment of 1 MeV H+, He+, and O+ projectiles was investigated. H+, H+2, H+3, C+, CH+2, CH+3, and Cl+ fragments were observed and their respective kinetic energy spectra recorded. Results suggest that one particular channel involved in the dissociation is CH3Cl2+→CH+3+Cl+ with a dissociation energy of 6.6 eV. Results also indicate a possible mechanism in CH+n production involving the dissociation of a CHnClm+ fragment.

Dissociation of CO and NO by fast H+, He+, and O+ projectiles

In this work we report on studies of the dissociative ionization of CO and NO induced by 1‐MeV H+, He+, and O+ projectiles. The time‐energy spectroscopy (TES) technique is used to identify the dissociation fragments according to their mass‐to‐charge (m/q) ratios, and to record kinetic energy spectra for each fragment species. The spectra fragments with 1+, 2+, and 3+ charges show overlapping peaks for which energy assignments are made. In most case, the He+ and O+ projectiles appear to form dissociative states of CO2+ and NO2+ which decay into singly charged fragments. The H+ projectile appears to form CO+ and NO+ which subsequently dissociate into charged and neutral fragments. The dissociative states excited in this experiment are different from those reported in K‐shell ionization studies.

The dissociative ionization of CO2 by fast heavy ions

The time–energy spectroscopy (TES) technique has been used to study the dissociative ionization of CO2 induced by bombardment with 1 MeV H+, He+, and O+ ions. Fragments observed in the dissociation process include C+, O+, CO+, C2+, and O2+. The technique used permits separation and identification of the different fragment species, and measurement of a kinetic energy spectrum for each species. The kinetic energy spectra and relative intensities of the different fragments are reported. The O+ ions constitute more than half of the total charged fragment yield. The C+ and CO+ yields are nearly equal and the yield of doubly charged ions is small. The energy spectra and yields are compared to electron impact and neutral helium impact dissociation studies. The O+ and CO+ data suggest that the channel (CO2)2+→CO++O++6.0 eV is a major contributor to the observed spectra.

Coincidence detection of dissociative fragments from CH3Cl

In this letter, we describe the results of the detection, in coincidence, of CHn+ and Cl+ ions which result from the dissociation of CH3Cl after bombardment by 1 MeV He+ projectiles. The results confirm the existence of four dissociation channels, each with a kinetic energy release 0f 6.6 eV. The results suggest the channels could be due to a process in which 0, 1, 2,, or 3 hydrogens are dissociated from the methyl chloride and the remaining CH+n and Cl+ dissociate by a breaking of the carbon–chlorine bond. (AIP)

Molecular Dissociation Produced by Fast Heavy Ion Bombardment

A technique has been developed to study the dissociative ionization of molecules by fast, heavy ions. A pulsed beam of projectiles is focused into a differentially-pumped chamber containing a gaseous, molecular target. The fragment ions from the molecular target are investigated by measuring their kinetic energy and their time-of-flight (TOF) from the collision region to a detector. The simultaneous measurement of kinetic energy and TOF separates the fragments according to their mass-to-charge ratios and yields the kinetic energy spectrum of each. This time-energy spectroscopy method has been applied to several diatomic molecules and methane. Dissociative states of molecules and ionizing collisions by different projectiles have been investigated.

Dissociative ionization of N2O produced by 1 MeV H+, He+, O+ projectiles

N2O is bombarded with 1 MeV H+, He+, and O+ projectiles. The dissociation fragments observed are N+, O+, NO+, N2+, N2+, and O2+. Kinetic energy spectra of singly ionized fragments obtained using a time‐energy spectroscopy TES technique are reported. The relative intensities and the absolute yields of these fragments are dependent on the type of projectile which is used to bombard the target gas. Bombardment with O+ projectiles produces the most absolute yield and enhances the yield of 5 to 10 eV fragments relative to the yield of 0 to 5 eV fragments. These spectra are interpreted and a comparison is made to electron impact and photoionization studies of N2O by other groups. This study indicates that the dissociation channels N2O2+→NO+ + N+ and N2O2+→ N2+ +O+ are probable major contributors to the yields of NO+ and N2+. In addition, the O+ and N+ spectra exhibit high energy tails which may be attributed to multibody break up.