xraytools.

Isotope Pattern

https://xraytools.com/isotopes?formula=CH2Br2

No diffraction data

The distribution of molecular masses that the natural isotopic composition of the elements produces — the M, M+1, M+2 series a mass spectrum shows — together with the monoisotopic and average mass.

You supply
A chemical formula, in the same grammar every other page here uses. Whole atoms only: a pattern describes one molecule, so a fractional stoichiometry is refused rather than rounded. Write a charge into the formula (SO4^2-, Na+) and every mass becomes m/z, electron mass included.
Reading it
This is an exact combinatorial result, not a simulated spectrum: no resolution, no peak shape, no adducts and no fragmentation. Which peak is tallest is not the monoisotopic one for tin or a polybrominated compound, and the chart says what its heights are measured against.

Worked examples: a nickel complex · dibromomethane · tin tetrachloride · a sulfate anion

See also: Absorption Coefficient Calculator · CHN Calculator

What each input changes
Show peaks above
The floor, as a percentage of the tallest peak, below which a peak is left out of the table. Between 0.001 and 100: above 100 nothing would be listed, and at 0 a large molecule lists thousands of combinations no spectrometer separates.

Input

Write the charge into the formula if you want m/z: SO4^2-, [Fe(CN)6]^3-, Na+.

% of the tallest

A height relative to the tallest peak, so it runs from 0.001 to 100 %. Lower it to see the weak peaks; raise it to see only the ones an instrument would pick out.

Results

formula: CH2Br2
monoisotopic mass: 171.8523
average mass: 173.8337
base peak: 173.8503

Pattern

Isotope pattern, 4 peaks. The table below carries the same numbers.0255075100171.8523 Da, 172 nucleons: 51.40 % of the base peak, 25.414 % of the whole pattern171.8523 · 51.4 %173.8503 Da, 174 nucleons: 100.00 % of the base peak, 49.444 % of the whole pattern173.8503 · 100.0 %174.8537 Da, 175 nucleons: 1.10 % of the base peak, 0.546 % of the whole pattern174.8537 · 1.1 %175.8482 Da, 176 nucleons: 48.64 % of the base peak, 24.049 % of the whole pattern175.8482 · 48.6 %172173174175176mass / Darelative abundance / %
Every peak of the pattern above, and the isotopes that make it. CSV
massnucleonsrelative / %abundance / %made of
171.8523 172 51.40 25.414 monoisotopic 100.0 %
173.8503 174 100.00 49.444 81Br 100.0 %
174.8537 175 1.10 0.546 13C + 81Br 97.9 %, 2H + 81Br 2.1 %
175.8482 176 48.64 24.049 2 81Br 100.0 %

These are the relative abundances that follow from the natural isotopic composition of the elements — an exact combinatorial result, not a simulated spectrum. There is no instrument here: no resolution, no peak shape, no adducts and no fragmentation. Combinations with the same number of nucleons are shown as one peak at their abundance-weighted mass, which is what an instrument of ordinary resolving power sees; at high resolution several of these would split. Abundances are relative to the tallest peak, which is not always the monoisotopic one. Point at a peak or at its row to mark both; click to keep it marked, and click it again or press Escape to let go.

The last column names the isotope substitutions each peak is made of, as percentages of that peak, counted from the composition in which every element takes its most abundant nuclide — the same composition the monoisotopic mass is defined from. Two substitutions with the same nucleon count are one peak here and two different molecules in a high-resolution spectrum. Where a peak has more combinations than the column lists, the rest are summed as other combinations, so the percentages always add up to 100.

Where this comes from