The Elusive Bound OH-Stretching First Overtone of Water Dimer

Area of Science:

• * Molecular spectroscopy
• * Atmospheric chemistry
• * Quantum chemistry

Background:

• * Water dimer is a key hydrogen-bound complex in atmospheric studies.
• * The bound OH-stretching fundamental transition is well-characterized.
• * The first overtone of this transition was theoretically predicted to be very weak.

Purpose of the Study:

• * To experimentally observe the previously elusive first OH-stretching overtone transition in water dimer.
• * To compare experimental results with recent theoretical predictions.
• * To characterize the spectral properties and lifetime of this transition.

Main Methods:

• * Jet expansion cavity ring-down spectroscopy was employed.
• * Measurements were conducted in the spectral region predicted by theoretical calculations.
• * Full-dimensional ro-vibrational calculations informed the experimental search.

Main Results:

• * The first OH-stretching overtone transition of water dimer was successfully observed.
• * Experimental data (wavenumber, intensity, band shape) closely matched new theoretical predictions.
• * A broad, relatively unstructured band was observed due to overlapping transitions.
• * The vibrational band origin was determined to be 7049 cm^-1.
• * An estimated lifetime of approximately 10 ps was determined.

Conclusions:

• * The experimental observation validates revised theoretical predictions for the water dimer OH-stretching first overtone.
• * This finding enhances understanding of hydrogen-bound complexes and their atmospheric relevance.
• * The study demonstrates the capability of advanced spectroscopic techniques to probe weak transitions.