Some comments on the thermodynamics of sonoluminescence — a personal view

The path of the gas in a sonoluminescent bubble must enclose an area in a P-V plot if the gas itself emits photons. Thermodynamic analysis thus delineates the playing field that may enable us to distinguish liquid-phase emissions from gas-phase emissions. The apparent importance of the van der Waals a (which parameterizes mean-square induced dipole attractions) in light intensity supports collision-induced emission as a likely mechanism. The suggested emitting object, containing 1010 molecules in picosecond-long van der Waals contact, is novel, being neither plasma, gas, liquid nor blackbody. The bubble pursues a unique thermodynamic path.