calculation of the intensity ratio of the 84/86/88 peaks of Dichloromethane?

Question

I had a practical on mass spectral fragmentation patterns of some organic compounds and had a table to fill in to show the m/z, formula of ion and fragmentation diagram. I have done that but there is also a calculation to be done but i dont know how to do it. As the teachers are also unavailable and i have to hand this in tomorow i am unable to find out how to do it.
So please anyone who may know or has done this practical before please help and i will very much appreciate it.
when i did this practical i got on the graph for CH2Cl2 there were a total of 13 peaks.
i am only told to calculate the intensity ratio for three peaks.
Thank you
Regards

Answer 1

The natural isotopes:
12C: 0.9893; and 13C: 0.0107
1H: 0.9999; and 2H: 0.0001
35Cl: 0.7576; and 37Cl: 0.2424
So for natural occuring isotopes, there seems only 8 different masses. So the population of 84-Dichloromethane:
P84 = 0.9893*0.9999^2*0.7576^2
The population of 86-Dichloromethane:
P86 = 0.9893*0.9999^2*(2*0.7576*0.2424) + 0.0107*(2*0.9999*0.0001)*0.7576^2 + 0.9893*0.0001^2*0.7576^2
The population of 88-Dichloromethane:
P88 = 0.0107*(2*0.9999*0.0001)*(2*0.7576*0.2424) + 0.9893*0.0001^2*(2*0.7576*0.2424) + 0.9893*0.9999^2*0.2424^2