Stabilities of complexes (N2)nH+, and (O2)nH+ for n = 1 to 7 based on gas phase ion-equilibria measurements

Abstract

The equilibria Bn−1H+ + B = BnH+ for B = N2, CO, and O2 were measured with a pulsed electron beam high ion source pressure mass spectrometer. Equilibria up to n = 7 could be observed. van't Hoff plots of the equilibrium constants lead to ΔGn−1,n0, ΔHn−1,n0, and ΔSn−1,n0. While the proton affinities increase in the order O2 < N2 < CO, the stabilities of the B2H+ towards dissociation to BH+ + B increase in the reverse order, i.e. CO < N2 < O2. The stabilities towards dissociation of B for BnH+ where n > 2 are much lower for all three compounds; however for N2 and CO the stability decreases only very slowly from n = 3 to n = 6, then there is a large fall off for n = 7. The (O2)nH+ clusters show large decrease of stabilities as n increases. The BnH+ (for n > 3) of CO are more stable than those of N2 or O2. The above experimental results can be partially explained with the help of results from molecular orbital STO-3G calculations for B, BH+, and B2H+ and general considerations. BH+ and B2H+ for CO and N2 are found to be linear while those for O2 are bent. The most stable O2H+ is a triplet, while (O2)2H+ is a quintuplet.