Spin Tunneling in Mn-12 Cannot be Assisted by Phonons at Millikelvin   Temperatures [Comment on PRL 83, 416 (1999) by Bellessa et al]
  Recently, Bellessa et al in a Physical Review Letter entitled "Phonon-Assisted Tunneling in High-Spin Molecules: Experimental Evidence", reported observation of a peak in the imaginary part of the ac-susceptibility of Mn-12 molecular nanomagnet, that decreases strongly below 0.1 K down to 0.02 K. They explained this effect by a "phonon-induced tunneling process". The purpose of this Comment is to show that the explanation of Bellessa et al is logically inconsistent and physically impossible. All formulas in the Letter supporting that explanation are incorrect. 
E. M. Chudnovsky and D. A. Garanin