Amos S. Newton

Determination of the Excitation Functions for Formation of Metastable States of Some Rare Gases and Diatomic Molecules by Electron Impact

An apparatus for the determination of the excitation functions for formation of metastable states by impact of electrons of precisely defined energies in the energy range from threshold to the ionization potential is described. Results are given for Ne, Ar, Kr, H2, N2, and CO. Two sharp resonances are observed in each of the rare‐gas excitation functions, which correspond to excitation with electron exchange of the first two excited configurations of these atoms. For diatomic molecules, no such resonances are observed, except in nitrogen, where there is a resonance process with an onset energy of 11.8 eV. A partial explanation for the shapes of the excitation functions is offered, based on the location and character of the various excited triplet states of the molecules studied.

Metastable Dissociation of the Doubly Charged Carbon Monoxide Ion

The metastable dissociation of CO2+ ions has been studied. The appearance potentials of CO2+ (M / q = 14) and the O+ and C+ daughter products were found equal at 41.5 ± 0.4 eV. The kinetic‐energy release was found to be 5.75 ± 0.2 eV. The half‐life was 20 + 10 or − 5 μsec, and no CO2+ ions of half‐life longer than this were observed. It is concluded that the metastable dissociation of CO2+ proceeds via a tunneling mechanism consistent with previous suggestions in this regard.

Metastable State of the Doubly Charged Carbon Dioxide Ion

A metastable state in CO2++ dissociating into CO++O+ with a half‐life of 2.3±0.2 μsec has been observed. The corresponding metastable peaks are observed at (M1/q1)*=35.6 and (M2/q2)*=11.6, respectively. The widening of these peaks with accelerating voltage shows the repulsion energy to be 2.7 eV and the corresponding charge separation at fragmentation to be 5.3 A. The appearance potential of CO2++ was found to be 38.0±0.2 eV, and this value is discussed in terms of the various repulsion energies and energy balances. The data is consistent with the hypothesis of an immediate fragmentation into CO+(2Σ) and O+ and the metastable fragmentation into CO+(2IIi) and O+. The fragmentation of CO2++ enriched in O18 has also been reinvestigated. It is shown that the unsymmetrical doubly charged molecule ion (CO16O18++) has a lower yield than the corresponding symmetrical molecule ions containing O16 and O18, respectively.

Metastable Species Produced by Electron Excitation of N2, H2, N2O, and CO2

A molecular beam is crossed by an electron beam to produce metastable molecules and fragments which are detected by electron ejection from a Cs3Sb cathode in a chamber operating at ultrahigh vacuum. Excitation functions for the production of H2(c3Πu) molecules and of photons from H2 are reported. The time‐of‐flight distribution of the slow group of H(2S) atoms from H2 has been measured and this differs from a previously reported distribution. Threshold‐energy and kinetic‐energy measurements have been made on the electronically excited fragments known to be produced in the dissociative excitation of CO2 and N2O. It is postulated that in CO2 the initial products are CO(a3II) and O−. A new excitation curve for the E3Σg+ state of N2 was determined.

Excess‐Kinetic‐Energy Ions in Organic Mass Spectra

The characteristics of excess‐kinetic‐energy ions in mass spectra have been studied with a Dempster‐type mass spectrometer. A method was devised whereby the total initial kinetic energies possessed by such ions could be measured more accurately than has been done previously, and the kinetic energies of methyl ions, both near‐thermal and excess‐kinetic‐energy, from a wide variety of different organic compounds, are presented. Appearance potential curves were obtained for several excess‐kinetic‐energy methyl ions; these show a second‐power dependence of cross section on electron energy in the threshold region with threshold values of the order of 30 eV. Finally, a method of estimating the discrimination factor of the mass spectrometer toward ions possessing excess kinetic energy was utilized to obtain values for the actual abundances of excess‐kinetic‐energy methyl ions in the fragmentations of several organic compounds. Actual abundances of from 2% to 10% of the total ions in the mass spectrum were found f...

Autoionization of Highly Excited Ar+ Ions Produced by Electron Impact

The (M/q)*=10 peak in the mass spectrum of argon observed at ionizing electron energies of 40 to 120 eV (uncorr.), is shown to consist of approximately equal contributions from: (1) surface‐induced transitions of an excited Ar+ ion to Ar2+ at the last ion‐source slit, and (2) an autoionization of an excited Ar+ ion after the last ion‐source slit. By use of an auxiliary slit beyond the last normal ion‐source slit, these two processes were separable, and it is shown that the excited state undergoing surface‐induced transitions is a different state than that undergoing autoionization, with the autoionizing state having an A.P. of 0.5±0.2 eV higher than the state undergoing surface‐induced transitions. The existence of autoionizing states of Ne+ and Ar2+ was also confirmed.

Metastable‐Ion Peak Shapes in Dempster‐Type Mass Spectrometers

The shape and position on the mass scale of the metastable peak at M*/q=31.88 in the mass spectrum of n‐C4H10 has been calculated and compared with the observed peak. The calculation was made on the assumption that the ion beamwidth, determined by the beamwidth of normal ions at the collector slit, was widened by velocity components added to the fragments from kinetic energy released in the fragmentation process. The only adjustable parameter used was the total kinetic‐energy release in the fragmentation, T. A value of T=0.015±0.005 eV gave the best fit of the observed peaks to the computed peaks. This value is compared with the literature values of T determined by different methods for this metastable dissociation.

The occurrence of the H3+ ion in the mass spectra of organic compounds

Abstract The H3+ ion is shown to be a normal component of low yield in the fragmentation pattern of organic compounds (except C2H2). The pattern of H3+ is tabulated for the 780 eV mass spectrum of each of 33 compounds of various types. Specific studies of the energetics of formation of H3+ from CH4, C2H6 and CH3Cl, and of D3+ from CD4 were conducted. The H3+ ion is shown to be derived from two sources, a low initial kinetic energy component which arises from fragmentation of the singly charged molecular ion and a high initial kinetic energy component whose appearance potential and kinetic energy release are consistent with fragmentation of the doubly charged molecular ion. Systematic variations of H3+ pattern factors with carbon number are shown for the n-alkanes and 1-alkenes and with halogen type for the series of methyl halides.

Surface‐Induced Transitions in Highly Excited Noble‐Gas Ions and Quasimetastable Peaks in the Mass Spectra of the Noble Gases

The appearance of some quasimetastable peaks in the mass spectra of the noble gases is shown to be due to a surface‐induced transition of the type: X(q)+*→ lim SX(q+1)++e− in which X is any of the noble gases and S represents a metal surface. In argon, peaks arising from this type of transition at the ion‐source first slit, focus slit, and last slit, respectively, have been observed and characterized as to (1) their behavior with the voltage effective at each respective slit, (2) their kinetic energy as measured by the metastable‐ion‐suppressor cutoff behavior, and (3) their appearance potential. These peaks are postulated to arise from ions in Rydberg levels of high principal quantum number at an excitation level near the next higher ionization potential. Possible mechanisms for the transition are discussed.

Electron impact excitation functions of radiating and metastable states of carbon monoxide

Abstract Excitation functions near threshold have been measured for the production of photons and for the production of long-lived metastable molecules from carbon monoxide. An interesting peaked feature exiss at the threshold for photon production.