Knowledge Bank

Previously we analyzed intracluster vibrational motions of $Arn$, $n13-55$, clusters by use of molecular dynamics $methoda$. It was shown that a number of collective vibrations were excited. The vibrations were assigned to breathing, quadruple spheroidal and quadruple torsional vibrations corresponding to the modes of a dense sphere with the radius of $Arn$ and the phonon velocities in solid Ar. Such vibrations were observed for Ar Clusters by the energy loss of colliding He $atomsb$. The frequencies of these vibrations were found to decrease with the incressing cluster size, suggesting that these vibrational motions are new physical properties of clusters obeying a scaling law. In this work, the motions of Ar atoms and $CO2$ molecule in $ArnCO2$ cluster produced by addition of $CO2$ to the surface of $Arn$ cluster, are simulated by use of the classical molecular dynamics method. The potential is calculated by overlapping two-body Lennard-Jones potentials, where an anisotropic potential is used for the Ar-$CO2$ interection. By extracting the breathing and quadruple spheroidal vibrations, the frequencies of these modes are calculated to be: e.g., 33 and $20cm-1$, respectively, for $Ar13CO2$. These values are almost indentical to those for $Ar13$. This indicates that the addition of $CO2$ causes little effect on the vibration of $Ar13$ when the $CO2$ molecule is on the surface of $Ar13$. Cluster-temperature and cluster-size dependence of the frequencies will be presented.