2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/84509Enrichment of nuclear spin isomers of molecules by infrared radiation resonant to molecular rovibrational transition is considered. Special attention is given to the enrichment by light-induced crossing of far separated ortho and para states.8 pages + 2 eps figures. REVTEX 4. Invited talk at the VIIth International Symposium on "Magnetic Field and Spin Effects in Chemistry and Related Phenomenon", 15-20 July 2001, Tokyo, JapanChemical Physicstext