# Lifetimes of He S=1,0 states

1. Jan 2, 2013

### Sekonda

Hey,

I have question on Helium with one electron in it's ground state orbital 1s and the other in the 2s orbital. We have S=1 states reffering to the spin symmetric triplet state and S=0 reffering to the spin antisymmetric singlet state, due to quantum effects of the electron-electron interactions we find that the energy of S=1 state and S=0 states are split by the direct and exchange components of the energy correction.

We find that S=1 states, where the spins are parallel, have lower energies than S=0 states - not sure of the physical interpretation of this - I'm guessing it's just because it's energetically favourable to have parallel spins further apart than having opposing spins in the same orbital.

Anyway, the S=1 states and S=0 states have very different lifetimes but I'm not sure what is meant by 'lifetimes' and why the lifetimes are different?

Thanks for any help,
SK

2. Jan 3, 2013

### andrien

there is an energy part due to spins containing S1.S2 which will give negative contribution to energy when spins are parallel and opposite for other.Can you tell where you have seen the lifetimes for them?(it is meant to be for decay)

3. Jan 3, 2013

### ycheff

Phys.Rev. 180 (69) 25-32
Phys.Rev.Lett. 26 (71) 681-684

23S1 -> 11S0 t=8000 sec
21S0 -> 11S0 t=19.5 msec

4. Jan 3, 2013

### andrien

Have you seen it is for helium ion,it's o.k. for them.

5. Jan 3, 2013

### ycheff

I don't know value for helium ion, for hydrogen atom:
22S1/2 -> 12S1/2 t= 2 msec

Last edited: Jan 3, 2013
6. Jan 4, 2013

### andrien

I said that values are for helium ion,not for helium atom.

7. Jan 5, 2013

### ycheff

Hydrogen atom (H I) is analog of helium ion (He II).
For He II:
22S1/2 -> 12S1/2 t > 1 msec (Bull. Amer. Phys. Soc, 1962, v. 7, p. 258)

8. Jan 6, 2013

### andrien

Oh no,I said For one electron atom it is useful.They are not for two electron atom as is helium atom.You seem to be more interested than O.P.