  The angular momentum quantum number L of spherical harmonic Y_l_,_m based on
an associated Legendre polynomial is nonnegative integer 0 1 2 ... and must
never be a fraction. But the study in this paper found that the quantum number
L corresponding to other series of solutions of the associated Legendre
equation should be fractions. This paper not only proposed the spherical
harmonics Y for L=1/2, but also spherical harmonics Y for L = 1/n = 1/3 1/4 1/5
... In addition to the spin s=1/2 of electron-like particles, the fractional
spin such as 1/3, 1/4, 1/5,...were boldly speculated to be verified in this
paper. Setting the spin of a particle with only two spin components of up and
down to s = 1/2 is not necessarily correct. Based on the symmetry of the plots
of Ys, three different spin classes of particles are predicted. The first class
of particles s = 1/2 1/6 ... resembles electrons, particles with the parallel
spins tend to move away from each other, and the second class of particles s =
1/3 1/5 ... does not repel each other regardless of whether their spins are
parallel or not, and the third class of particles s = 1/4 1/8 ... always repels
each other and tend to move away regardless of whether their spins are parallel
or not. The use of fractional spin can be well illustrated for electrons and
protons as reported in the literature. This view may be important for the study
of quantum mechanics and elementary practices.
