Laboratory measurement of the S(9) pure rotation frequency in H2

The frequency of the v = 0..-->..0,J = 11..-->..9 transition in molecular hydrogen has been measured in the laboratory using stimulated Raman spectroscopy of H/sub 2/ and CO in a methane-air flame. This is the first direct laboratory study of any of the high-J transitions in H/sub 2/ which have been observed in the Orion molecular cloud. The Orion measurements are consistent with the laboratory result, although the Orion frequencies exhibit a general positive offset of approximately 1 cm/sup -1/. Correcting for this offset, we have generated a new set of ground-state parameters for H/sub 2/. The laboratory frequency for S(9) is 2130.102(4) cm/sup -1/.