It is shown that the assignment of parity in previous works neglected the vector nature of the elastic field and thus the resultant selection rules are erroneous. We propose a correct selection rule: Among the vibration modes of a sphere, only the torsional mode with angular momentum $l=1$ is observable by infrared absorption and the torsional mode with $l=2$ is observable by Raman scattering. The spheroidal modes cannot be observed by infrared or Raman spectroscopy in the dipole approximation.

• Received 22 June 2005

DOI:https://doi.org/10.1103/PhysRevB.72.241405