Selective alignment of molecular spin isomers

We experimentally demonstrate field-free, spin-selective alignment of ortho- and para molecular spin isomers at room temperature. By means of two nonresonant, strong, properly delayed femtosecond pulses within a four wave mixing arrangement, we observed selective alignment for homonuclear diatomics composed of spin 1/2 (N-15) or spin 1 (N-14) atoms. The achieved selective control of the isomers' angular distribution and rotational excitation may find applications to analysis, enrichment, and actual physical separation of molecular spin modifications.