A. F. Sciamanna

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.

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.

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.

On the metastable dissociation of the CH+ ion produced by electron impact

The metastable dissociation of CH+ and CD+ ions has been investigated. CH+(m) from CH4, C2H2, C2H4, CHCl3, CH2Cl2, and CD+(m) from CD4, C2D2, C2D4, and CDF3 were studied. CH+(m) and CD+(m) dissociate with an apparent half‐life of 0.4± 0.2 × 10−6 sec and with kinetic energy release in the dissociation of 1.1±0.3 and 1.4±0.3 eV, respectively. Using 70 eV electrons, CD+(m) and CH+(m) are formed with initial kinetic energy, the value being dependent on the compound irradiated. Appearance potential measurements show that when formed from C2H2 and C2D2, the CH+(m) and CD+(m) must dissociate to the lowest dissociation limit of CH+, i.e., C+(2P1/20) and H(2S). It is postulated that the metastability arises from a predissociation of the b 3Σ− state with the repulsive c 3Σ+ state of CH+.