A CHARGE-TRANSFER COMPLEX CH-3+-AR IN THE GAS-PHASE

The thermochemical data DELTA-H(n-1,n)0 and DELTA-S(n-1,n)0 for clustering reactions CH3+(Ar)n-1 + Ar reversible CH3+(Ar)n were determined with a pulsed electron beam high-pressure mass spectrometer. It was found that (1) the bond energy of CH3+(Ar)n with n = 1 (-DELTA-H0,1(0) = 11.3 kcal/mol) is much higher than that with n = 2 (-DELTA-H1,2(0) = 2.26 kcal/mol); (2) -DELTA-H1,2(0) is slightly greater than -DELTA-H2,3(0) (1.97 kcal/mol), and (3) the -DELTA-H(n-1,n)0 values with n = 3-8 are almost n-independent. The structures of CH3+ (Ar)n with n = 1-3 were determined by ab initio MO calculations. The theoretical calculations predict some participation of covalent bond (charge transfer) in CH3+(Ar)n with n = 1 and 2. The nature of bonding in the complex with n greater-than-or-equal-to 3 is almost entirely electrostatic.