Gas-phase nuclear magnetic relaxation in Xe-129 revisited

In this contribution gas-phase Xe-129 spin-lattice relaxation time measurem ents are extended to conditions (pressure, temperature, magnetic-field stre ngth, isotope composition) not previously used. It is shown that wall effec ts become apparent at densities below similar to 20 amagat, and that these become dominant below similar to3 amagat. A significant new discovery from field-dependent studies is that, in addition to the previously identified f ield-independent spin-rotation relaxation operative in the bulk gas, there is a contribution from the modulation of the chemical shift that depends on the square of the applied magnetic-field strength. The weak temperature de pendence of the relaxation times can be understood in terms of the opposite temperature coefficients of the field-independent and field-dependent cont ributions to the relaxation. The spin-rotation contribution and its tempera ture dependence are calculated and found to be in good agreement with the e xperimental data. The low field, low density limit for the relaxation time is 56.3 +/-2.6 hr.amagat at 295 K in the absence of wall effects. (C) 2001 American Institute of Physics.