Methanol (Me) adsorbs intact on copper, silver, and gold clusters at 70 K to form the complexes Cu n Me m , Ag n Me m , and Au n Me m , respectively. The infrared photodissociation spectra of the deuterium-substituted complexes M n (CD 3 OH) m and M n (CD 3 OD) m (M n ) Cu 3-11 , Ag 3-22 , and Au 3-13 ) have been recorded in the 9-11 µm region. The methanol C-O stretching band frequency is invariant with cluster size and depends only slightly on the metal of which the underlying cluster is composed, indicating that local interactions are responsible for the shift from the gas-phase value and that these interactions are similar for methanol adsorbed on clusters of all three metals. Progressive blue shifts of the depletion bands of Ag n Me m and Au n Me m with increasing m indicate a strong interaction among methanol ligands in these species.

Ethylene and ethylene oxide react readily with silver clusters at 70 K to form the addition complexes, Agn(C2H4)m and Agn(C2H4O)m, respectively. The infrared photodissociation spectra of Agn(C2H4)m and Agn(C2D4)m (n=3–7) recorded in the 9–11 μm region show several characteristic vibrational bands of ethylene lying near their gas phase frequencies. Photoionization spectroscopy studies reveal that the ionization potentials (IPs) of the complexes decrease monotonically with adsorption of additional ethylene molecules. Together, these results imply that as on macroscopic silver surfaces, ethylene adsorbs molecularly to small silver clusters, with a net donation of electron density into the underlying cluster. Similarly, silver cluster–ethylene oxide complexes display IPs that decrease with increasing adsorbate coverage. The infrared depletion spectra of Agn(C2D4O)m complexes reveal a single feature at 949 cm−1, assigned to the ν4(a1) fundamental of C2D4O. These results verify that ethylene oxide adsorbs molecularly to silver clusters, with the oxygen atom oriented toward the silver cluster.

Iron clusters react sequentially with hydrogen molecules to form multiply hydrogenated products. The increases in cluster ionization potential upon reaction verify that hydrogen chemisorbs dissociatively to form iron cluster-hydride complexes, Fe n H m . At low source temperatures, the cluster-hydride complexes take up additional hydrogen molecules which are shown to be physisorbed onto the underlying Fe n H m complexes to form Fe n H m (H 2 ) p species. The infrared spectra of Fe n H m and Fe n D m ͑nϭ9 -20) were obtained by the photodissociation action spectroscopic method in which depletion of the Fe n H m (H 2 ) p and Fe n D m (D 2 ) p species was the signature of absorption. The spectra, recorded in the 885-1090 cm Ϫ1 region, consist of several overlapping bands, each approximately 20 cm Ϫ1 in width. The dissimilarity of each Fe n H m (H 2 ) p spectrum with the corresponding Fe n D m (D 2 ) p spectrum indicates that the carrier involves hydrogen and is not merely due to absorption by the underlying iron cluster. Density functional calculations were performed on model complexes, Fe 13 H 14 and Fe 13 D 14 , the iron portion of which was assumed to have T h symmetry. The infrared-active vibrational frequencies involving hydrogen bending and deuterium stretching are predicted to lie within the experimental frequency range of the experiment, well removed from the skeletal modes of the underlying iron cluster. The complexity of the observed spectra as compared to simulations based on the assumed ͑high-symmetry͒ model imply that the experimentally produced complexes possess low symmetry.

The photoionization spectra of manganese clusters consisting of between seven and sixty-four atoms have been measured near threshold. As for other transition metal clusters previously investigated, the ionization potentials (IPs) decrease rapidly but nonmonotonically up to n≅20 and more slowly and smoothly beyond that. No correlation is observed between Mnn IPs and their reactivity toward molecular hydrogen, reported previously by Parks et al. [J. Chem. Phys. 104, 3531 (1996)]. In particular, the absence of any discontinuity in IP at Mn16 suggests that the onset of reactivity toward hydrogen noted at that size is not due to a sudden change in electronic structure (e.g., a nonmetal-to-metal transition), but rather to a change in cluster geometry.

The reactivity of selected Co n Mn m (8 ≤ m + n ≤ 23) clusters with N2 and the vertical ionization potentials (IPs) of selected Co n Mn m (8 ≤ m + n ≤ 31) clusters have been measured. No obvious correlation is found between the reactivities and the IPs. Inferences about cluster structure may be made from the nitrogen uptake data. In particular, whereas pure cobalt clusters tend to adopt structures having bulk packing, incorporation of manganese atoms into the cluster shifts the relative energies of close-lying isomers to favor an icosahedral growth sequence. For many cluster sizes, the maximum number of nitrogen molecules adsorbed on a cluster at −80 °C is equal to the number of cobalt atoms on the surface of the cluster, thereby giving insight into the cluster structure and the locations of the individual cobalt and manganese atoms in these bimetallic species.