Evidence of nuclear-spin symmetry violation in molecular collisions is
presented. Measurements of the ortho-para conversion rates in (CH3F)-
C-12 embedded in an gaseous oxygen or nitrogen shows that oxygen speed
s up the nuclear spin conversion by 2 x 10(-4) s(-1)/Torr contrary to
nitrogen which slows down the conversion by 1 x 10(-4) s(-1)/Torr. The
difference is attributed to direct collisional transitions between th
e ortho and para states in CH3F due to the large oxygen magnetic momen
t, which is much smaller in the case of nitrogen. (C) 1998 Published b
y Elsevier Science B.V. All rights reserved.