What part of spherical harmonic coefficients represents physics quantities?

[susantha]

Hi,
I need expand a spherical function(real function not a complex function) in terms of spherical harmonics. Expansion coefficients are complex numbers. If i need to observe physics quantities that are represented by the spherical harmonics coefficients which part should i look at- real part, complex part or the magnitudes (sqrt(real^2 + imaginary^2) of spherical harmonic coefficients?

Thanks in advance

 

[DrDu]

You can combine the two spherical harmonics with same l but m and -m to get two real functions just like you can combine exp(ix) and exp(-ix) to obtain cos(x) and sin(x). These new functions form a real basis which you can use. You have probably seen them in the representation of the chemists orbitals.