Da. Wood et al., COLLISIONAL ACTIVATION DYNAMICS OF OH-(H2O)(N) CLUSTER IONS - COMPARISON TO H3O+(H2O)(N), Journal of physical chemistry, 98(50), 1994, pp. 13138-13143
The collisional activation dynamics of hydrated hydroxide clusters in
a fast ion beam have been studied upon multiple glancing collisions wi
th argon. Glancing collisions are defined as those involving detectabl
e parent or fragment ions at the end of the beam line. Hydrated cluste
r ions are ideal for multiple-collision studies because one glancing c
ollision will not on average impart enough energy to dissociate the cl
uster while two such collisions predominantly lead to dissociation. Th
e absolute values of the attenuation cross section of OH-(H2O)(n=0-4)
with argon are 31.6(1.8), 29(2), 25.2(1.4), 33(2), and 50(10) Angstrom
(2), respectively. The absolute values of the glancing collision induc
ed dissociation cross sections are 1.17(0.08) Angstrom(2) for OH-(H2O)
(1) and 5.7(0.4) Angstrom(2) for OH-(H2O)2. The fraction of single gla
ncing collisions which do not lead to dissociation or loss from the io
n beam is 0.92 for OH-(H2O)(1) and 0.25 for OH-(H2O)(2). Single-collis
ion branching ratios of 0.88:0.12 and 0.52:0.46:0.02 have been determi
ned for successive loss of waters from OH-(H2O)(2) and OH-(H2O)(3), re
spectively. Detachment gives way to dissociation upon collisional acti
vation as several waters are clustered to OH-. Comparison of the hydra
ted hydroxide attenuation cross sections vs cluster size to those of h
ydrated hydronium and hard sphere expectations implies that the excess
charge of OH- is more localized in water clusters than the proton.