Stabilities of complexes (N₂)_<i>n</i>H⁺, and (O₂)_<i>n</i>H⁺ for <i>n</i> = 1 to 7 based on gas phase ion-equilibria measurements

Abstract

The equilibria B n−1 H + + B = B n H + for B = N 2 , CO, and O 2 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 ΔG n −1,n 0 , ΔH n −1,n 0 , and ΔS n −1,n 0 . While the proton affinities increase in the order O 2 &lt; N 2 &lt; CO, the stabilities of the B 2 H + towards dissociation to BH + + B increase in the reverse order, i.e. CO &lt; N 2 &lt; O 2 . The stabilities towards dissociation of B for B n H + where n &gt; 2 are much lower for all three compounds; however for N 2 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 (O 2 ) n H + clusters show large decrease of stabilities as n increases. The B n H + (for n &gt; 3) of CO are more stable than those of N 2 or O 2 . The above experimental results can be partially explained with the help of results from molecular orbital STO-3G calculations for B, BH + , and B 2 H + and general considerations. BH + and B 2 H + for CO and N 2 are found to be linear while those for O 2 are bent. The most stable O 2 H + is a triplet, while (O 2 ) 2 H + is a quintuplet.