title: Vibrationally excited ultrafast thermodynamic phase transitions at the water/air interface.
abstract: The extraordinary ability of the hydrogen-bond network of water in the condensed phase to thermalize vibrational excitations within several picoseconds, even under supercritical conditions, offers the possibility of creating highly excited thermodynamic states at water surfaces on ultrafast time scales using vibrationally resonant short infrared laser pulses. We experimentally and numerically studied such states created by depositing ~100 ps long pulses tuned to the 3400 cm(-1) O–H stretch vibration at the water/air interface using time-resolved dark-field imaging and time-resolved optical reflectivity. The results are reasonably well described by using a hydrodynamic ablation model under the assumption of impulsive heat deposition. The large thermoelastic stress amplitudes on the order of 1 GPa created within 100 ps by depositing laser pulses with ~1 J cm(-2) fluence were inferred from the numerical simulations. Stresses of this magnitude drive the excited water layer into a very fast expansion resulting in rapid adiabatic cooling and thorough vaporization within a few nanoseconds. The spatial and temporal lengths scales of the ablation plume are nearly ideal for ejecting molecules into the gas phase with minimum perturbation for applications ranging from mass spectrometry and laser surgery to the development of extremely high pressure molecular beams.
authors.affiliation: Departments of Physics and Chemistry and the Institute for Optical Sciences, University of Toronto, 60. St. George Street, Toronto, Ontario M5S 1A7, Canada.
authors.forename: Kresimir
authors.initials: K
authors.lastname: Franjic
authors.forename: Dwayne
authors.initials: D
authors.lastname: Miller
mesh_terms: D000388:Air; D006860:Hydrogen Bonding; D007834:Lasers; D008962:Models, Theoretical; D056004:Molecular Dynamics Simulation; D044367:Phase Transition; D013816:Thermodynamics; D013997:Time Factors; D014732:Vibration; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water