Depth-Profiling and Diffusion Measurements in Ice Films Using Infrared Laser Resonant Desorption

Abstract

A new infrared laser resonant desorption (LRD) technique has been developed that permits depth-profiling and diffusion measurements in ice. This LRD technique utilizes an Er:YAG rotary Q-switched laser with an output wavelength of lambda = 2.94 microm and a pulse duration of approximately 100 ns. The Er:YAG laser light resonantly excites O-H stretching vibrations in the H2O molecules that form the ice. This laser resonant heating induces H2O desorption at the ice surface. Control experiments were conducted on pure and isotopically mixed laminated ice films to determine the optimum experimental parameters for the LRD depth-profiling and diffusion measurements. Depending on laser energy, the measured desorption depth was either less than, comparable to, or larger than the optical penetration depth of approximately 0.8 microm at lambda = 2.94 microm. LRD studies were used to analyze H2 18O/H2 16O stacked multilayers and laminate sandwich structures. These measurements revealed that the LRD technique can depth-profile into ice films with submicrometer spatial resolution and high sensitivity. Two types of experiments employing LRD depth-profiling were demonstrated to monitor diffusion in ice. HCl hydrate diffusion in ice was measured versus time after depositing ice/HCl/ice sandwich structures. Na diffusion into ice was studied after adsorbing Na using a continuous Na source for a given exposure time at the diffusion temperature.

A review of air–ice chemical and physical interactions (AICI): liquids, quasi-liquids, and solids in snow

“…This was corroborated by the work of Domine et al (2001), who used infrared spectroscopy to show that the high concentrations used considerably perturb the ice structure, rendering it almost amorphous, so that the diffusion coefficients measured are not those of crystalline ice. Indeed, Livingston et al (2000) report D HCl = 5 × 10 −14 m 2 s −1 at 170 K, an unrealistically high value, compared to values in the range 10 −16 to 10 −15 m 2 s −1 at 238-265 K found by Thibert and Domine (1997). The profiling techniques discussed above are destructive, rendering direct in situ observation of the diffusion process difficult.…”

“…Infrared laser resonant desorption has also been used to study diffusion of HCl in ice (Livingston et al, 2000). The beauty of the technique is that laser ablation resolves subµm ice thicknesses, compared to ≈ 20 µm for serial sectioning of crystals mechanically.…”

“…Hence, experiments on shorter timescales seem possible. In the experiments presented by Livingston et al (2000) HCl dopant concentrations were high enough to form hydrates in the ice, and hence cannot be directly applied to the diffusion of dilute trace gases in the thermodynamic stability domain of ice. This was corroborated by the work of Domine et al (2001), who used infrared spectroscopy to show that the high concentrations used considerably perturb the ice structure, rendering it almost amorphous, so that the diffusion coefficients measured are not those of crystalline ice.…”

FTIR spectroscopic studies of the simultaneous condensation of HCl and H2O at 190 K – Atmospheric applications

“…Livingston et al (2000), using very high HCl concentrations, have measured diffusion coefficients of HCl in ice of the order of 5 × 10 −11 cm 2 /s at 190 K. This is several orders of magnitude higher than what could be reasonably envisaged for a solid so far from its melting point, and is much higher than other measured values (Dominé and Xueref, 2001;Thibert and Dominé, 1997;Wolff et al, 1989). Dominé and Xueref (2001) have demonstrated that the high values measured by Livingston et al (2000) were caused by the high HCl concentrations, that led to ice amorphization. The resulting disordered solid then allowed much faster diffusion of impurities.…”

A new modeling tool for the diffusion of gases in ice or amorphous binary mixture in the polar stratosphere and the upper troposphere

“…During the last decade, new infrared-laser resonant desorption (LRD) techniques have been employed to derive diffusion coefficients by depth profiling of ice films George, 1999, 2001;Livingston et al, 1997Livingston et al, , 1998Livingston et al, , 2000Livingston et al, , 2002Krasnopoler and George, 1998). These measurements revealed two different rate categories for bulk diffusion in ice.…”