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Ice surfaces are used to assign five resonances in the hydrogen-bonded vibrational spectrum of water. Ice surface experiments are complemented with room temperature matrix isolation experiments providing compelling evidence that the OH vibration of the donor is affected by the environment around the lone pairs, i.e., compelling evidence for the importance of three-body interactions. In addition, longer-range, correlated motion produces a quadrupole at the ice surface.

Students are frequently presented with novel visualizations introducing scientific concepts and processes normally unobservable to the naked eye. Despite being unfamiliar, students are expected to understand and employ the visualizations to solve problems. Domain experts exhibit more competency than novices when using complex visualizations, but less is known about how and when learners develop representational fluency. This project examined students' moment-by-moment adoption patterns for scientific visualizations. In a laboratory experiment, introductory-level organic chemistry students viewed familiar ball-and-stick and novel electrostatic potential map representations while solving chemistry problems. Eye movement patterns, verbal explanations, and individual difference analyses showed that students initially relied on familiar representations, particularly for difficult questions. However, as the task unfolded, students with more prior knowledge began relying upon the novel visualizations. These results indicate adoption and fluent use of visualizations is not given; rather, it is a function of prior knowledge and unfolding experience with presented content.

A major challenge in hydrogen-bond research is interpreting the vibrational spectrum of water, arguably the most fundamental hydrogen bonding system. This challenge remains despite over a half century of progress in vibrational spectroscopy, largely due to a combination of the huge oscillator strength and the enormous width of the hydrogen-bond region. Lack of assignment of the resonances in the hydrogen-bond region hinders investigation of interactions between water and solutes. This lack-of-interpretation issue is an even more significant problem for studies of the aqueous interface. Numerous solutes are known to have an effect, some very dramatic, on the shape of the surface spectrum. These effects, however, are but tantalizing teasers because lack of interpretation means that the changes cannot be used to diagnose the effect of solutes or impinging gas-phase molecules on the surface. In the reported work two techniques are used to probe the origin of vibrational resonances in the H-bonded region: the surface sensitive technique sum frequency generation (SFG) and room-temperature matrix isolation spectroscopy (RT-MIS). A polarization technique called polarization angle null (PAN) has been developed that extends SFG and enables identification of resonances. The result of applying PAN–SFG to single crystal, I h ice is identification of at least nine underlying resonances and assignment of two of these. One resonance is correlated with the crystal temperature and is a sensitive probe for interactions that disrupt long range order on the surface – it is a morphology reporter. The second is associated with weakly bonded, double-donor water molecules. This resonance is sensitive to interaction of hydrogen bond donors, i.e. acids, with the surface. Both modes are more correctly pictured as collective modes. These two assignments are the first definitive assignments in the hydrogen-bond region for the aqueous surface . The effect of salts on the vibrational spectrum of water is also probed with a recently developed room-temperature, matrix-isolation technique. The matrix environment demonstrates that salts containing large anions with small cations support water–water hydrogen bonds with a vibrational resonance that has similar characteristics as the SFG spectra of salt solutions.

In this work we present the vibrational spectrum of a hydrogen-bonded complex, nitric acid–water, in the region 6000–11 000 cm −1 using Fourier-transform infrared spectroscopy. This study builds on previous observation of the nitric acid–water complex in the mid-infrared via a carbon tetrachloride matrix to investigate the vibrational overtone region of the complex at ambient conditions. Our experimental observations of ν OH = 1, 2 and 3 of the nitric acid–water complex provides a testing ground for the simple harmonically coupled anharmonic oscillator local-mode model treatment of OH-vibrational overtone spectra of hydrogen-bonded complexes.

Sum frequency generation (SFG) vibrational spectroscopy along with the molecular probe, methanol, has been used to investigate the surface chemistry of TiO2. Methanol on TiO2 has two adsorption modes: a molecular physisorption mode and a dissociative chemisorption mode. Doping TiO2 with iron leads to quenching of the dissociative adsorption. Electron paramagnetic resonance (EPR) spectra of iron-doped TiO2 particles (particle size > 100 nm) compared to the same particles leached with water show that at least some of the iron is located on the surface. Particles are also characterized with UV–visible spectroscopy.

Knowledge of hydroxide ion’s spectral signature is an essential ingredient for finding it at the water surface. In solutions, the intense hydrogen-bonded resonance of water often hinders unambiguous characterization of the OH − stretching frequency and linewidth. These parameters are likely to be modified at the hydrophobic water–vapor interface. This communication reports the first experimental observation of hydroxide ion that is free from interaction with bulk water. OH − is isolated in a hydrophobic environment and exhibits a sharp resonance at 3634 cm −1 , as confirmed by isotopic substitution. The feature is red shifted from that of dangling OH bonds by 29 cm −1 .

The Raman spectra of aqueous ammonia solutions have been obtained between -40 and 25 degrees C. The Raman spectrum of neat water was also obtained at 25 degrees C and is characterized by two broad peaks observed at 3200 and 3400 cm(-1). The spectrum due to water is subtracted to determine the NH(3) spectrum at all temperatures. In ammonia-water solutions, the spectrum shows three features at measured displacements of 3250, 3316, and 3400 cm(-1). The feature at 3316 cm(-1) is assigned to the Q branch of the symmetric stretch. The broad, weak features at 3250 and 3400 cm(-1), previously assigned to rotational bands, are assigned to combination bands. The NH(3) combination bands are assigned by comparing with sum frequency generation (SFG) experiments, monitoring changes with temperature, and analyzing the polarization data. The rotational structure of the Q band is also discussed. As the temperature is lowered from 25 to -40 degrees C, an increase in the Raman intensity is observed for all bands. The relative Raman scattering cross section is determined from the numerically integrated area of the NH(3) Q branch at each temperature. Copyright 2001 Academic Press.

Sum frequency generation spectra indicate that the surface water of liquid sulfuric acid solutions varies as a function of concentration, but not with temperature. At 0.1 x H 2 SO 4 (where x =mole fraction, 38 wt%), subsurface ionic species orient surface water molecules. The surface of 0.2 x H 2 SO 4 (58 wt%) solutions, however, features H 2 SO 4 /H 2 O complexes both at 273 K and supercooled at 216 K. The results support a picture of stratospheric chemistry in which sulfuric acid aerosols are coated with hydrogen-bonded water/sulfuric acid complexes.

The influence of dissolved HCl on the surface of water has been investigated with sum frequency generation (SFG) spectroscopy. Ions in solution cause water on the surface to be reoriented relative to pure water, with hydrogen atoms directed toward the bulk solution. There is no signal due to molecular HCl suggesting that oriented water molecules, not molecular HCl, dominate the surface. A model is proposed to account for the reported SFG results as well as surface tension and surface potential measurements. The result suggests that application of the Gibbs equation to determine surface excess may need to be reevaluated.

Sum frequency generation (SFG) is used to obtain the vibrational spectrum of aqueous ammonia solution. The SF spectrum of concentrated solutions is dominated by the N–H symmetric stretch (ν1) at 3312 cm−1 and a weaker deformation mode (2ν4) at 3200 cm−1. The free OH peak of water is suppressed, compared to pure water, and the hydrogen-bonded region (3000–3450 cm−1) has interference in the presence of ammonia molecules at the interface. In dilute solution, ν1 is less intense and the free OH peak of water appears. These observations confirm the existence of an ammonia–water complex at the liquid/vapor interface.

The vibrational structure of water at the air/solution interface of an ionic solution has been obtained for the first time. Using vibrational sum frequency generation it is determined that ions in solution have a large orientational effect on the structure of the surface water. Electrolytic solutions, ionic in nature, cause water to be oriented into a more regular hydrogen-bonded network through an electric double layer at the interface. In electrolytic solutions where molecular or associated H 2 SO 4 or Cs 2 SO 4 species dominate, the surface water molecules are bound into hydrate complexes. These effects are explained using hard soft acid base (HSAB) theory.

Energy transfer in methyl isocyanide following i.r. multiphoton excitation has been examined with a CARS probe. Results show that CARS is an effective technique both for measuring the fraction of molecules receiving energy from the laser and for monitoring intermolecular energy transfer following laser irradiation. In addition, the Raman transition at 2169 cm −1 shows a vibrational progression due to hot bands of the ν 8 bend. Since the ν 8 , bend is the only low energy mode of the molecule, it is an effective vibrational “thermometer”. Utilizing this thermometer, results show that the vibrational state distribution does not fit a Boltzmann distribution for 7 μs following i.r. multiphoton excitation.