The shift from 1653 to 1668cmϪ1 for CϭO stretching band and from 1564 to about 1539cmϪ1 for N–H bending band was attributable to the gradual breaking of intermolecu- lar hydrogen bonds between acetaminophen molecules in- duced by the increase of temperature. A sharp peak at 1512 cmϪ1 shifted from 1506cmϪ1 was also observed, might be in- tensified by the N–H bending band of 1539cmϪ1.