The ion kinetic energy spectra of some aromatic hydrocarbons

The technique of ion kinetic energy spectroscopy has been applied to the study of the aromatic hydrocarbons benzene, toluene, naphthalene, 2-methyl naphthalene, biphenyl and anthracene. The method is illustrated by a complete study of naphthalene in which transitions of metastable doubly- and singly-charged ions are listed, including reactions in which singly-charged ions are formed by collision induced charge-exchange reactions of doubly-charged ions and by the double process of charge-exchange and metastable decomposition with loss of one or two hydrogen atoms. Decompositions of doubly-charged ions into two singly-charged ions, together with the kinetic energies released in these decompositions, are also given for all the compounds studied.     

The ion kinetic energy and mass spectra of isomeric methyl indoles

The mass spectra of the seven isomeric methylindoles were recorded and the [metastable ion]/[daughter ion] ratios for the reactions m/e 130 → m/e 103 and m/e 103 → m/e 77 have been obtained. The ratios indicate that the decomposing [M — 1] ions (m/e 130) from the 4, 5, 6 and 7 isomers are energetically similar as are the [M — 1] ions from the 2 and 3 isomers. The results observed for the m/e → 103 m/e 77 reaction showed that the decomposing m/e 103 ions from the 2, 3, 4, 5, 6 and 7 isomers all have the same energy distribution. N-Methylindole gave ratios which were similar to the 4 to 7 isomers at 70eV but different at 20 eV. The ion kinetic energy (IKE) spectra of all the isomeric methylindoles were also obtained and the results compared with the data obtained from the [metastable ion]/[daughter ion] approach. The results from the IKE spectra indicated that the energy distributions of the [M — 1] and [(M — 1) — HCN] ions from 1-methylindole and the [(M — 1) — HCN] ions from 2-methylindole could readily be distinguished from other isomers whose [metastable ion]/[daughter ion] ratios were similar. Thus by using both techniques certain ambiguities can be resolved.     

Interference peaks in mass analysed ion kinetic energy spectra

When mass analysed ion kinetic energy spectroscopy is performed on ions of low abundance and low mass compared with the rest of the ions present in the ion chamber, severe interference may be observed. The major form taken by the interference is of narrow peaks at non-integral mass numbers. Many such peaks can be observed in mass analysed ion kinetic energy spectra and they are mainly attributed to decompositions of metastable ions occurring in the first field free region of the reversed geometry double focusing mass spectrometer.     

The mass spectra of some chlorinated pesticidal compounds

The mass spectra of nine bridged polycyclic chlorinated pesticidal compounds have been investigated, and fragmentation modes to account for the more abundant ions are postulated. The principal features of the spectra are ions corresponding to a set of retro-Diels-Alder decompositions, ions resulting from successive losses of Cl, HCl, or both, ions produced by combinations of a retro-Diels-Alder process with a preliminary or subsequent loss of Cl or HCl, and ions whose processes of formation more specifically involve the epoxide group.     

Further interference peaks in mass analysed ion kinetic energy spectra

It is shown that interference peaks in mass analysed ion kinetic energy spectra can also occur from ions decomposing in the accelerating region of the ion source.     

Negative chemical ionization mass spectra of polycyclic chlorinated insecticides

Negative ion mass spectra obtained under chemical ionization conditions (NCI) employing methane, isobutane or methylene chloride as the enhancement gas are presented for a series of chlorinated polycyclic insecticides. All of the compounds examined except 1-hydroxychlordene yielded molecular anions of substantial relative abundance (6 to 39%). The most significant features of the spectra are the prominent peaks at masses greater than that of the molecule ion formed via ionmolecule association reactions. Peaks representing association of the parent molecule with ionic species such as H?, O?, OH?, Cl?, H₂OCl?, HCl₂?, ClO? and Cl₃? were observed in some cases. The base peak in all spectra was associated with the isotopic group of the [M + Cl]? on if contributions from other negative, even electron ions of low mass values present in high concentrations (Cl?, H₂OCl? Cl₂? and HCl₂?) are neglected. Fragmentation processes were limited to elimination reactions involving loss of combinations of the even electron neutral species H, Cl and HCl. In addition, fragmentation resulting from a nucleophilic radical displacement of Cl by O? from the parent molecule was observed in all cases except 1-hydroxychlordene when the source was modestly wet (methane as reactant gas). NCI mass spectra of polycyclic chlorinated pesticides are reproducible, intense, interpretable in terms of classical carbanion chemistry and thus may have important analytical utility, particularly when used in conjunction with positive electron-impact and chemical ionization mass spectral methods and selective use of different enhancement gases.     

The mass spectra of some chlorinated aromatic pesticidal compounds

Mass spectral studies of some chlorinated aromatic pesticidal compounds are reported. The compounds studied include substituted diphenyl derivatives of methane, ethene and methanol. The diphenylmethanes are characterized by a relatively intense peak at m/e 165. Comparison of their low voltage spectra with 9-dichloromethylfluorene indicates that this ion has a fluorenyl ion structure. The structure of the base peak (m/e 246) of the diphenylethenes was investigated by comparing competitive metastable transitions with 9-dichloromethylenefluorene and utilizing defocusing metastables. Additional studies of model compounds suggest that the m/e 246 ion is very complex and is probably comprised of a number of structures. The mass spectra of the diphenylmethanols are significantly different from the other two groups. The hydroxyl group markedly affects the fragmentation process for these compounds; the characteristic peak is presumably the chlorobenzoyl ion and is probably precursor for other fragment ions. Mass spectral correlations of pesticidal compounds of similar structure are needed to obtain enough background to facilitate interpretation of the mass spectra of their metabolites. Furthermore, such studies make feasible the identification of characteristic product ions formed by rearrangement processes during ionization of organic molecules in the gas phase. This information can be a nucleus for correlating the other significant mass spectral data of an unknown compound. Intensive studies of carbamates,¹ organophosphorus² and bridged polycyclic chlorinated pesticidal³ compounds were invaluable in identifying metabolites of the aforementioned pesticides.^4,5,6 The compounds in this Work are chlorinated aromatic pesticidal compounds which consist of a diphenylemthane, a diphenylethylene, or a diphenylmethanol structure. The compounds p,?-DDE were briefly discussed by Jorg, Houriet and Spiteller.⁷ The compounds examined are listed in Table 1. Treatment of data. The mass spectra of the pesticides are presented as bar graphs in Figs 1 to 12 It a metastable peak is observed, the metastable transition is indicated by m^* on the figures and also by (m^*) when confirmed or identified using the defocusing technique.⁸ Since the relative abundances of the metastable peaks for these compounds are very small (<0.1%) on special effort was made to establish their presence unless they wre pertinent.     

The ion kinetic energy spectra of isomeric chlorobenzenes and polychlorinated biphenyls (PCB'S)

The ion kinetic energy (IKE) spectra of the isomeric di-and trichlorobenzenes have been examined and the data for the latter compounds suggested that there was incomplete chlorine randomization in their molecular ions in the first field-free region of the mass spectrometer. Previous studies on the mass spectra and [metastable ion]/[daughter ion] ratios of the di-, tetra- and hexachlorobiphenyls (PCB's) indicated chlorine randomization in the molecular ions of those isomers containing less than two chlorine groups ortho to the Ph-Ph ring junction. In contrast the IKE spectra of the isomers are different and the results indicate incomplete chlorine randomization in the first field-free region of the mass spectrometer. These spectral differences may be of some use in PCB analysis.     

Charge localization: The ion kinetic energy spectra of pyrazine,pyrimidine and pyridazine

The ion kinetic energy (IKE) spectra of pyrazine, pyrimidine, pyridazine, pyrazine-d₄, pyrimidine-d₄ and pyridazine-d₄ have shown that these compounds can more readily be distinguished on the basis of IKE spectra than mass spectra. Studies of the fragmentation of various doublycharged ions have given information about the localization of charge on the heteroatoms and on the structures of the ions themselves. Transition states from which fragmentation occurs for doublycharged ions with loss of either [H]⁺ or [D]⁺ have shown large differences of the order 1 Å between the intercharge distances in the two cases.     

Ferrocene compounds: XVI. Mass-analyzed ion kinetic energy (MIKE) spectra of some monosubstituted ferrocene derivatives

The mass-analyzed ion kinetic energy (MIKE) spectra of some monosubstituted ferrocenes having an unsaturated moiety in the α- or β-position to the cyclopentadienyl ring and β-phenyl-γ-ferrocenoylbutyric acid are presented and discussed.     

Charge localization—I The ion kinetic energy spectra of ortho-, meta- and para-phenylenediamine

The ion kinetic energy spectra of o-,m-and p-phenylendiamine are presented. Decompositions of doubly-charged ions are given for the three isomers. From the width of the peaks, the energy released is measured and the equivalent intercharge distance is calculated. The results are discussed in terms of possible structures of the various ions. Also, metastable transitions which could give rise to peaks corresponding to energies below that of the mainion beam are listed and the results discussed. Significant differences were observed among the energy spectra of the three isomers.     

Comparative study of ion kinetic energy,chemical ionisation and field desorption spectra

A comparison of the fragmentation processes operating in the first field free region was made with the fragmentation in the ion source under electron ionisation, chemical ionisation and field desorption conditions for some selected compounds which undergo retro-DielsI-Alder fragmentation in the ion source under electron ionisationconditions. The fragmentation processes which com-ete with retro-Diels-Alder fragmentation under chemical ionisation and field desorption conditions are discussed. The complementary nature of these techniques are illustrated.     

A data acquisition system for mass-analyzed ion kinetic energy spectra using a personal computer

An inexpensive data acquisition system has been developed for mass-analyzed kinetic energy experiments which involve scanning the electrostatic analyzer of a reversed geometry mass spectrometer. The various hardware and software design features are described. Results for data obtained with a commercially available VG ZAB-2F mass spectrometer are presented and discussed.     

Carbon-13 NMR spectra of some chlorinated polycyclodiene pesticides

Carbon-13 NMR spectra have been obtained for aldrin, dieldrin, isodrin, endrin, heptachlor, heptachlor oxide and 24 of their degradation/conversion products. Chemical shifts were assigned on the basis of (1) comparison among the spectra, (2) single frequency, off-resonance decoupling experiments, (3) substituent effects derived for norbornanes and (4) spectra obtained with an added lanthanide shift reagent. The substituent effects previously reported for norbornanes were found to be applicable for establishing trends in the chemical shifts for many of the compounds studied.     

The structure of the ion: An ion kinetic energy spectrometry study

The kinetic energy release (T) values for the loss of CO from ions from five compounds have been obtained and are consistent with at least two different structures for the ion. This result is supported by the T value obtained for the decomposition of the molecular ions.     

The benzoyl ion. Thermochemistry and kinetic energy release

The thermochemistry of benzoyl ion formation from a variety of sources has been examined by using the measured kinetic energy release for metastable ions to estimate the excess energy of the activated complex. A correlation is observed between this estimated excess energy and literature values of the heat of formation of the benzoyl ion. From this relationship and the observed correlation between the uncorrected heat of formation and the difference between the appearance potential of [C6H5CO]⁺ and the ionization potential of the parent compound, the large range of reported values for ΔHf[C6H5CO]⁺ is seen to be due, at least in part, to variation in the kinetic shift with the critical energy of the reaction. With the exception of the ion generated from trifluoroacetophenone and possibly that from benzaldehyde, the fragmenting [C7H5O]⁺ ions are shown, from kinetic energy release data, to be structurally identical. The approach adopted here may have general merit in improving or testing the accuracy of thermochemical data based on appearance potential measurements.     

How to measure the kinetic energy distribution of the precursor ion main beam in mass-analyzed ion kinetic energy spectrometry experiments

Scans of the electrostatic analyzer (ESA) across the precursor ion beam in reverse-geometry (BE) mass spectrometers that are operated under double-focusing conditions do not measure the “energy resolution of the main beam”: They only measure double-focusing resolution. The only way that ESA scans can measure the kinetic energy distribution of the main beam is to operate the instrument so that angular (directional) focusing is not achieved. Thus, the mass spectrometer is no longer double-focusing. Under double-focusing conditions, however, scans of the accelerating voltage while the magnetic field and ESA are held constant can be used to measure either the kinetic energy distribution of the main beam that enters the magnet or the energy-resolving power of the instrument. Scans at a constant ratio of B²/E can be used similarly. The energy-resolving power of any ESA is defined by its dispersion and the widths of the energy-resolving object and image slits that immediately precede and follow the ESA, respectively. The use of BE, EB, and triple-sector instruments to measure energy-resolving power and the kinetic energy distribution of the precursor ion main beam is compared and discussed.