A new assignment of the signals in the 23Na DOR N M R spectra to the different sodium sites in dehydrated NaY zeolite is presented. 23Na DOR and MAS N M R measurements of dehydrated N a y , Ca2+-exchanged NaY samples, and NaY samples in which M o ( C O )~ is adsorbed are used for this purpose. Four distinct signals in the 23Na DOR N M R spectra of dehydrated NaY are found: the first signal with an isotropic chemical shift of -6 ppm and a quadrupolar coupling constant of 0.4 M H z is assigned to

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... the Na+ cations at site I. The second signal, with an isotropic chemical shift of -12 ppm and a quadrupolar coupling constant of 2.3 MHz, is assigned to the Na+ cations at sites I'/II'. The third and the fourth signals, with isotropic chemical shifts of -4 and 5 ppm and quadrupolar coupling constants of 4.2 and 4.7 MHz, respectively, are assigned to the Na+ cations at sites I1 and 111.