The slow, laser-induced coalescence of two conjoined, polystyrene spheres levitated in a quadrupole ion trap is investigated by monitoring optical morphology dependent resonances (MDRs) appearing in the fluorescence emission spectrum. The heated bisphere is driven by surface tension to become a single, larger sphere with a volume equal to the combined volumes of the two initial spheres. In the final stage of the structural transformation the particle is a prolate spheroid whose dimensions are ascertained by analyzing frequency shifts of the non-degenerate azimuthal MDRs. The relaxation time for the deformed viscous sphere is used to estimate the polystyrene viscosity and temperature. The study highlights the feasibility of using a temperature-controlled quadrupole ion trap to investigate the coalescence dynamics of viscous microstructures free from the perturbative effects of any solvent or substrate. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.