Effect of liquid temperature on sonoluminescence

Computer simulations of bubble oscillations are performed under conditions of sonoluminescence (SL) in water for various liquid temperatures. It is clarified that at almost all acoustic amplitudes, the bubble temperature at the collapse is higher in a colder liquid because a lesser amount of water vapor is trapped inside a bubble at the collapse due to the lower-saturated vapor pressure. Accordingly, at relatively low-acoustic amplitudes, the SL emissions from plasma inside a bubble are much stronger in a colder liquid. However, at higher-acoustic amplitudes, the SL emission originates in chemiluminescence of OH and the intensity is smaller in a colder liquid because a lesser amount of excited OH radicals are created inside a bubble. In actual experiments of multibubble sonoluminescence (MBSL) in water, the light consists of plasma emissions from low-acoustic amplitude region and chemiluminescence of OH from high-acoustic amplitude region. Usually, MBSL in a colder liquid is stronger because of the much stronger plasma emissions. The liquid-temperature dependence of single-bubble sonoluminescence is also discussed.