Single droplet displacement infrared action spectroscopy

Area of Science:

• Physical Chemistry
• Analytical Chemistry
• Environmental Chemistry

Background:

• Aqueous microdroplets exhibit unique properties distinct from bulk solutions.
• Characterizing microdroplet chemistry is challenging due to limited single-droplet spectroscopic data.
• Existing methods lack the precision to analyze individual microdroplets effectively.

Purpose of the Study:

• To introduce a novel spectroscopic technique for analyzing single aqueous microdroplets.
• To enable precise IR spectral measurements of individual microdroplets.
• To demonstrate the technique's capability in identifying supersaturated salt solutions.

Main Methods:

• Developed Single Droplet Displacement Infrared Action Spectroscopy (SiDDIRAS).
• Trapped individual microdroplets using a linear quadrupole electrodynamic balance.
• Measured IR-induced mass loss by detecting droplet displacement as a function of IR frequency.

Main Results:

• Successfully recorded the IR spectrum of a single ~8 µm microdroplet.
• Observed a 5 cm⁻¹ blueshift and peak broadening in the azide asymmetric stretch for NaCl and NaN₃.
• The spectral changes indicate supersaturation of salts within the microdroplet compared to bulk solutions.

Conclusions:

• SiDDIRAS is a powerful new tool for microdroplet analysis.
• The technique provides evidence of supersaturation in single microdroplets.
• SiDDIRAS has broad potential applications in various chemical disciplines.