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# Spectroscopy q watch

1. The mass spectrum of CH3Br contains two molecular peaks of equal abundance with m/z values of 94 and 96. Deduce the number of molecular ion peaks in the spectrum of the compound CH2Br2, Give their relative abundances and the m/z value of the molecular ion with the greatest mass.

The answers are 79Br and 81Br, and CH2Br2 has 3 peaks with relative abundances 11, the m/z values are 172, 174 and 176.

I don't understand how am I supposed to know how many peaks there are? How do I work out the abundances too?
2. (Original post by Magenta96)
The mass spectrum of CH3Br contains two molecular peaks of equal abundance with m/z values of 94 and 96. Deduce the number of molecular ion peaks in the spectrum of the compound CH2Br2, Give their relative abundances and the m/z value of the molecular ion with the greatest mass.

The answers are 79Br and 81Br, and CH2Br2 has 3 peaks with relative abundances 11, the m/z values are 172, 174 and 176.

I don't understand how am I supposed to know how many peaks there are? How do I work out the abundances too?
You are expected to recognise that bromine has two isotopes with approximate abundances of 50% ...

Statistically with two atoms of bromine you have double the possibility of 79Br81Br than 79Br79Br or 81Br81Br, so the peak height is 11
3. (Original post by charco)
You are expected to recognise that bromine has two isotopes with approximate abundances of 50% ...

Statistically with two atoms of bromine you have double the possibility of 79Br81Br than 79Br79Br or 81Br81Br, so the peak height is 11
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