Gallium arsenide, GaAs, has gained widespread use in...

Gallium arsenide, GaAs, has gained widespread use in semiconductor devices that convert light and electrical signals in fiberoptic communications systems. Gallium consists of $60 . \%^{69} \mathrm{Ga}$ and $40 . \%^{71} \mathrm{Ga}$. Arsenic has only one naturally occurring isotope, $^{75} \mathrm{As}$. Gallium arsenide is a polymeric material, but its mass spectrum shows fragments with the formulas $\mathrm{GaAs}$ and $\mathrm{Ga}_{2} \mathrm{As}_{2} .$ What would the distribution of peaks look like for these two fragments?

Key Concepts

Fragmentation Patterns

Fragmentation patterns describe how a compound breaks into smaller pieces under ionization conditions in a mass spectrometer. The specific ways in which molecular bonds break determine which ionic fragments appear in the spectrum and at which masses, helping to infer structural information about the original compound.

Statistical (Binomial) Distribution

When a molecule contains elements with multiple isotopes, the combinations of these isotopes in a fragment occur in proportion to their natural abundances. The probability of each isotopic combination, and hence the intensity of the corresponding peak in the mass spectrum, can be predicted using a binomial or multinomial statistical distribution.

Isotopic Abundance

This concept refers to the natural relative percentages of an element’s isotopes. In mass spectrometry, the different isotopes contribute to the formation of peaks at different masses because each isotopic variant has its own atomic mass. The observed peak intensities in a mass spectrum of a compound like a semiconductor depend directly on these isotopic abundances.

Mass Spectrometry

Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of ionized fragments. It is used to determine the molecular weight, structure, and composition of compounds by analyzing the pattern of mass peaks corresponding to various ion fragments formed upon ionization.

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