# Reduced mass?

1. Apr 6, 2008

### astrosona

[SOLVED] reduced mass?!

Hi there,

I know the reduced mass is defining with the below formula:

$$\frac{1}{\mu}$$ = $$\frac{1}{m _{1}} + \frac{1}{m_{2}} + ...$$

In Bohr's radius when i want to find the $$\mu$$ i use the
m1 = mass of electron
m2 = mass of poroton

but what if i need to find the reduced mass of a molecule like HCI ?
do i have to take the masses of all electrons and protons the molecule has or do i have to just take the masses of C & H & I?

I need it to solve the problem 1.5 page 26 from book: Modern Spectroscopy by Hollas

thanks
sona

Last edited: Apr 6, 2008
2. Apr 8, 2008

### astrosona

ok, i found the answer myself!

yes! i was correct! the reduced mass of molecules are been calculated as what i thought the other day. we just use the mass of the atoms without thinking of the protons and electrons...actually the mass of the atom is the real mass not the reduced mass. The point is for the big molecules like HCl or .... the difference between the reduced mass calculated by taking the real mass of element atoms or the reduced mass of the elem atoms is too small to be considered.

so for example for HCl: (1/ miu) = (1/mass of H) + (1/ mass of Cl)

cooooooooool! ha?