RADICAL IONS OF ACETYLENE IN ZSM5 ZEOLITES - AN EPR AND THEORETICAL-STUDY

The cis-bent form of the acetylene radical anion (a(iso)(H) = 65 G) wa s observed following radiolysis of acetylene-loaded HZSM5 but not NaZS M5. The acetylene radical cation is not trapped by the matrix at 77 K and undergoes ion-molecule reactions to form multimer ions, including the benzene cation. Benzene is also formed by acid-catalyzed polymeriz ation of acetylene on HZSM5. The evidence that acetylene (IP = 11.4 eV ) is ionized places a new lower limit on the range of ionizable specie s in the radiolyzed zeolite. The energies, geometries, and hyperfine c oupling constants were calculated for the acetylene, vinylidene, cyclo butadiene and butatriene radical anions and radical cations, and the b enzene radical cation, using different levels of theory, including gra dient-corrected density functional theory.