Appearance potential spectrum

The energy difference between diazirine and diazomethane, interesting from the point of view of their isomerism, came from MS measurements (63JCP(39)3534). The appearance potentials of the CH2 ion, common to both compounds, yielded a difference in heats of formation of 125kJmor A strong peak in the mass spectrum of 3-chloro-3-methyl-diazirine (50) with relative mass 55 was ascribed to the methyldiazirinium ion (51). 

In the electron impact mass spectrum of C02, 0+ ions are formed with an appearance potential (AP) 19.1 e.v. according to the process ... 

Fio. 12. Fhotoelectron spectrum of methanol vapour using the helium resonance line (21-21 e.v.). Ionization energy increases from left to right. The adiabatic ionization potentials measured (Al-Jobomy and Turner, 1964) are indicated by vertical arrows, and can be compared with (probably) vertical I.P. values derived from electron impact appearance potentials by Collin (1961) (dotted arrows). 

The results of elctron-impact studies of phosphine by Halmann et al. are given in Table 3a. The authors used the appearance potentials, in conjunction with thermochemical data, to choose the probable reaction processes. In many simple cases the observed appearance potential A (Z) for an ion fragment Z from a molecule RZ is related to its ionisation potential 7(Z) and to the energy of dissociation 7)(R—Z) of the bond by the expression A (Z) = /(Z) + D (R—Z). This assumes that the dissociation products are formed with little, if any, excitation energy, and that /(Z) < /(R). The most abundant ion species in the usual mass spectrum of phosphine is PH, which is probably formed according to the following mechanism... 

Winters and Kiser have reported appearance potentials and cracking patterns for Ni(CO)4 (243), Fe(CO)5 (243), and the Group VI hexacar-bonyls (244). These carbonyls fragment by a series of consecutive uni-molecular reactions with loss of neutral CO groups. Support for this scheme came from an investigation of the metastable transitions in the spectrum of Fe(CO)5 (242), which were observed for the following processes ... 

An early report (131) of the spectrum of Mn2(CO)10 mentioned no parent ion, but only strong peaks due to Mn2(CO)+ (n=5, 6, and 7) together with other weaker carbonyl-containing ions. More recently, appearance potentials and cracking patterns for Mn2(CO)10 and Co2(CO)8 were reported (247) and the spectra of Mn2(CO)10 and Re2(CO)i0 have been compared (49, 164). 

Metal alkyls also form aggregates, and the association of LiC2H5 has been investigated by the technique of mass spectrometry. The ions found in the mass spectrum consist of Li R + with n= 1 to 6. However, the appearance potentials (which are associated with the ease of producing these ions) are considerably lower than for ions having other composition. Therefore, it was concluded that the equilibrium in the vapor is predominantly... 

It has been studied by IR spectroscopy (when trapped in a low-temperature matrix) and by mass spectrometric studies on the vapor. Isotopic studies ( Cl/ Cl and 0/ 0) allow the 0-P-Cl bond angle to be calculated from the IR spectra at ca. 105° (i.e. close to the bond angle of CH2PCI). From the observed appearance potential (20.9 eV) of P+ [AP(P+)j in the mass spectrum of OPCl, it is possible to estimate the enthalpy of atomization of OPCl(g) via the Bom Haber cycle (Scheme 6). Hence, since the standard enthalpies of formation of P(g), 0(g), and Cl(g) are all known, the standard enthalpy of formation of OPCl(g) [A // 9g(OPCl)] may be estimated as -250.7 kJmol . ... 

The flash vacuum pyrolysis and the mass spectrometric fragmentation of a series of five methyl substituted phenanthrenes were correlated with each other in a quaUtatively predictable way.i ) The major thermochemical products for these compounds generally corresponded to one of the five most intense fragment ions in the compound s electron impact mass spectrum. The importance of products which corresponded to ions with high appearance potentials increased with increasing temperature in the thermolysis system. 

Electron impact measurements of the appearance potentials of various ions in the mass spectrum of methylamine and other amines by Collin 2 lead to upper limits to Z)(GN) in these compounds which appear to be very much larger than the most probable values. These probable values are not directly determined, but can be obtained from the heats of formation of the amines and the radicals concerned. Collin, for example, gives 140 kcal as an upper limit to D(CH -NH2), whereas the most probable value is about 80 kcal. 

The HBO ion has been detected mass spectrometrically by Sholette and Porter (2.) and Farber and Frisch (2). However, no appearance potential data have been reported for the ion. Kroto et al. ( ) recently attempted to measure the photelectron spectrum of HBO by passing water vapor over heated boron. The spectrum showed no bands which could be definitely assigned to HBO monomer. Unfortunately, the region of their spectrum ( 14-15 eV) where the first photoelectron band of HBO would be expected to lie shows a broad band which also appeared In the spectrum of HBS above 1150"C. Kroto et al. 4) have assigned this band to dlborane. He believe the HBO band may well be hidden under this broad band. 

Our thermal functions Indicate that PF" is thermodynamically stable with respect to dissociation (P + F") below 2500 K. These predictions agree qualitatively with the results of MacNeil and Thynne ( ) who observed PF" in the negative ion mass spectrum of PF. Their reported appearance potential, AP(PF"/PFg) = 11.4 0.1 eV, gives EA(PF) = -0.47 eV assuming that the dissociative electron capture process is PF (g) + e" = PF"(g) + 2F(g). We believe this value is too low probably because of excess kinetic and/or excitation energies amounting to roughly 1.5 eV. 

Energy spectrum of secondary electrons Appearance potential spectroscopy APS... 

The determination of further electron affinities is not an easy matter it is possible that the electronic equilibrium method could be extended to a few more elements, but at the temperatures involved, molecules and radicals would be decomposed. The only reasonable hope of estimating the electron affinities of radicals would seem to lie in a study of the appearance potential of negative ions, and the determination of their kinetic energies, although it must be borne in mind that a careful search of the mass spectrum of methane has failed to reveal the existence of a CH3(-)ion. [4]... 

The appearance potentials of a series of phosphine oxides (186 R = propyl, propenyl, or propynyl) are all similar to that of acetone, which supports the postulate that the predominant ionization is loss of an electron from oxygen. The fragmentation patterns were examined to see if there is a relationship with alkaline cleavage. The ion at m/e 92 is the base peak in the spectrum of (186 R = propyl) and is attributed to the... 

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