Vibrational spectra of water complexes with H2, N2, and CO

Understanding the high-resolution spectral signature of the N2-H2O van der Waals complex in the 2OH stretch region

We present the observation of the N2-H2O van der Waals complex in the 2OH stretch overtone region. The high-resolution jet cooled spectra were measured using a sensitive continuous wave cavity ringdown spectrometer. Several bands were observed and vibrationally assigned in terms of ν1, ν2, and ν3, the vibrational quantum numbers of the isolated H2O molecule, as (ν1'ν2'ν3')←(ν1″ν2″ν3″)=(200)←(000) and (101) ← (000). A combination band involving the excitation of the in-plane bending motion of N2 and the (101) vibration of water is also reported. The spectra were analyzed using a set of four asymmetric top rotors, each associated with a nuclear spin isomer. Several local perturbations of the (101) vibrational state were observed. These perturbations were assigned to the presence of the nearby (200) vibrational state and to the combination of (200) with intermolecular modes.

Effect of nitrogen molecules on the growth kinetics at the interface between a (111) plane of cubic ice and water

The molecular-scale growth kinetics of ice from water in the presence of air molecules are still poorly understood, despite their importance for understanding ice particle formation in nature. In this study, a molecular dynamics simulation is conducted to elucidate the molecular-scale growth kinetics at the interface between a (111) plane of cubic ice and water in the presence of N2 molecules. Two potential models of N2 molecules with and without atomic charges are examined. For both models, N2 molecules bind stably to the interface for a period of 1 ns or longer, and the stability of the binding is higher for the charged model than for the noncharged model. Free-energy surfaces of an N2 molecule along the interface and along an ideal (111) plane surface of cubic ice suggest that for both models, the position where an N2 molecule binds stably is different at the interface and on the ideal plane surface, and the stability of the binding is much higher for the interface than for the ideal plane surface. For both models, stacking-disordered ice grows at the interface, and the formation probability of a hexagonal ice layer in the stacking-disordered ice is higher for the charged model than for the uncharged model. The formation probability for the hexagonal ice layer in the stacking-disordered ice depends not only on the stability of binding but also on the positions where N2 molecules bind on the underlying ice, and the number of N2 molecules that bind stably to the underlying ice.

Spectroscopic study of the tunneling dynamics in N2-water observed in the O-D stretch region

The O-D stretch rovibrational spectra of N₂-D₂O and N₂-DOH were measured and analyzed. A combination band involving the in-plane N₂ bending vibration was also observed. These bands were recorded using a pulsed-slit supersonic jet expansion and a mid-infrared tunable optical parametric oscillator. The spectra were analyzed by considering the feasible tunneling motions, and transitions were fitted to independent asymmetric rotors for each tunneling state. The rotational constants of the four tunneling components of N₂-D₂O were retrieved for the excited vibrational states. A two order of magnitude increase in the tunneling splittings is observed for the asymmetric O-D stretch (ν₃ in D₂O) excitation compared to the symmetric stretch (ν₁ in D₂O) and to the ground vibrational state. This last finding indicates that the ν₃ vibrational state is likely perturbed by a combination state that includes ν₁. Finally, the observation of a local perturbation in the ν₃ vibrational band, affecting the positions of few rovibrational levels, provides an experimental lower limit of the dissociation energy of the complex, D₀ > 120 cm^-1.

Explicitly correlated ab initio potential energy surface and predicted rovibrational spectra for H2O-N2 and D2O-N2 complexes

An ab initio intermolecular potential energy surface (PES) for the van der Waals complex of H₂O-N₂ that explicitly incorporates the intramolecular Q₂ bending normal mode of the H₂O monomer is presented. The electronic structure computations have been carried out at the explicitly correlated coupled cluster theory [CCSD(T)-F12] with an augmented correlation-consistent triple zeta basis set and an additional bond function. Analytic five-dimensional intermolecular PESs for ν₂(H₂O) = 0 and 1 are obtained by fitting to the multi-dimensional Morse/long-range potential function form. These fits to 40 890 points have the root-mean-square (rms) discrepancy of 0.88 cm^-1 for interaction energies less than 2000.0 cm^-1. The resulting vibrationally averaged PESs provide good representations of the experimental microwave and infrared data: for microwave transitions of H₂O-N₂, the rms discrepancy is only 0.0003 cm^-1, and for infrared transitions of the A₁ symmetry of the H₂O(ν₂ = 1 ← 0)-N₂, the rms discrepancy is 0.001 cm^-1. The calculated infrared band origin shifts associated with the ν₂ bending vibration of water are 2.210 cm^-1 and 1.323 cm^-1 for H₂O-N₂ and D₂O-N₂, respectively, in good agreement with the experimental values of 2.254 cm^-1 and 1.266 cm^-1. The benchmark tests and comparisons of the predicted spectral properties are carried out between CCSD(T)-F12a and CCSD(T)-F12b approaches.

Structure and water attachment rates of ice in the atmosphere: role of nitrogen

In this work we perform computer simulations of the ice surface in order to elucidate the role of nitrogen in the crystal growth rates and crystal habits of snow in the atmosphere. In pure water vapor at temperatures typical of ice crystal formation in cirrus clouds, we find that basal and primary prismatic facets exhibit a layer of premelted ice, with thickness in the subnanometer range. For partial pressures of 1 bar, well above the expected values in the troposphere, we find that only small amounts of nitrogen are adsorbed. The adsorption takes place onto the premelted surface, and hardly any nitrogen dissolves within the premelting film. The premelting film thickness does not change either. We quantify the resulting change of the ice/vapor surface tension to be in the hundredth of mN m^-1 and find that the structure of the pristine ice surface is not changed in a significant manner. We perform a trajectory analysis of colliding water molecules, and find that the attachment rates from direct ballistic collision are very close to unity irrespective of the nitrogen pressure. Nitrogen is however at sufficient density to deflect a fraction of trajectories with smaller distance than the mean free path. Our results show explicitly that the reported differences in growth rates measured in pure water vapor and a controlled nitrogen atmosphere are not related to a significant disruption of the ice surface due to nitrogen adsorption. On the contrary, we show clearly from our trajectory analysis that nitrogen slows down the crystal growth rates due to collisions between water molecules with bulk nitrogen gas. This clarifies the long standing controversy of the role of inert gases on crystal growth rates and demonstrates their influence is solely related to the diffusion limited flow of water vapor across the gas phase.

An accurate full-dimensional permutationally invariant potential energy surface for the interaction between H2O and CO

The first full-dimensional accurate potential energy surface was developed for the CO + H₂O system based onca.102 000 points calculated at the CCSD(T)-F12a/AVTZ level using a permutation invariant polynomial-neural network (PIP-NN) method.

Incremental NH stretching downshift through stepwise nitrogen complexation of pyrrole: a combined jet expansion and matrix isolation study

The NH stretch of pyrrole experiences downshifts when expanded with N₂ or embedded in pure/mixed N₂ matrices, no blueshift.

Structural and spectroscopic characterization of DMF complexes with nitrogen, carbon monoxide, ammonia and water. Infrared matrix isolation and theoretical studies [corrected]

An infrared spectroscopic and MP2/6-311++G(2d,2p) study of the complexes between N,N-dimethylformamide (DMF) and nitrogen, carbon monoxide, water, ammonia trapped in solid argon matrices is reported [corrected]. The 1:1 molecular complexes have been identified in the DMF/B/Ar matrices (B=N₂, CO, H₂O, NH₃); their structures were determined by comparison of the spectra with the results of calculations. The analysis of the experimental and theoretical data indicate that the DMF-N₂, CO complexes present in the matrices are stabilized by (C=)O⋯N and (C=)O⋯C van der Waals interactions. In turn, in the DMF-H₂O, NH₃ complexes the (C=)O⋯H(OH) and (C=)O⋯H(NH₂) hydrogen bonding is present in which the carbonyl group of DMF acts as a proton acceptor. In all systems studied the C-H⋯X (X=N, C, O) bonding is a second intermolecular force stabilizing the planar complexes. Some spectral features indicate that for DMF-H₂O, DMF-NH₃ systems the nonplanar structures with the C=O⋯H interaction are also present. The study demonstrated the strong sensitivity of the CH stretching wavenumber to an involvement of the C-H and/or C=O groups of DMF in an intermolecular interaction.

VUV photochemistry of the H2O⋯CO complex in noble-gas matrices: formation of the OH⋯CO complex and the HOCO radical

VUV photolysis of the H₂O⋯CO complexes leads to the formation of the OH⋯CO radical–molecule complexes and trans-HOCO radicals.

Unveiling the Surface Structure of Amorphous Solid Water via Selective Infrared Irradiation of OH Stretching Modes

In the quest to understand the formation of the building blocks of life, amorphous solid water (ASW) is one of the most widely studied molecular systems. Indeed, ASW is ubiquitous in the cold interstellar medium (ISM), where ASW-coated dust grains provide a catalytic surface for solid phase chemistry, and is believed to be present in the Earth's atmosphere at high altitudes. It has been shown that the ice surface adsorbs small molecules such as CO, N2, or CH4, most likely at OH groups dangling from the surface. Our study presents completely new insights concerning the behavior of ASW upon selective infrared (IR) irradiation of its dangling modes. When irradiated, these surface H2O molecules reorganize, predominantly forming a stabilized monomer-like water mode on the ice surface. We show that we systematically provoke "hole-burning" effects (or net loss of oscillators) at the wavelength of irradiation and reproduce the same absorbed water monomer on the ASW surface. Our study suggests that all dangling modes share one common channel of vibrational relaxation; the ice remains amorphous but with a reduced range of binding sites, and thus an altered catalytic capacity.

From strong van der Waals complexes to hydrogen bonding: From CO⋯H2O to CS⋯H2O and SiO⋯H2O complexes

Structures and interaction energies of complexes valence isoelectronic to the important CO⋯H(2)O complex, namely SiO⋯H(2)O and CS⋯H(2)O, have been studied for the first time using high-level ab initio methods. Although CO, SiO, and CS are valence isoelectronic, the structures of their complexes with water differ significantly, owing partially to their widely varied dipole moments. The predicted dissociation energies D(0) are 1.8 (CO⋯H(2)O), 2.7 (CS⋯H(2)O), and 4.9 (SiO⋯H(2)O) kcal∕mol. The implications of these results have been examined in light of the dipole moments of the separate moieties and current concepts of hydrogen bonding. It is hoped that the present results will spark additional interest in these complexes and in the general non-covalent paradigms they represent.

Intermolecular potential energy surface and second virial coefficients for the nonrigid water-CO dimer

A seven-dimensional potential energy surface is calculated for the interaction of water and carbon monoxide using second-order Moller-Plesset theory, coupled-cluster theory, and extrapolated intermolecular perturbation theory. The effects of stretching the CO molecule and bending the water molecule are included. The minimum energy structure of the water-CO dimer changes from an H-C hydrogen bond to an H-O hydrogen bond when the CO bond length increases by less than 10 pm from its equilibrium value. Second virial coefficients for the water-CO interaction are calculated for a wide range of temperatures and compared with the limited experimental data. Allowing the CO bond length and water bond angle to vary has little effect on the second virial coefficients.

Infrared spectra and intensities of the H2O and N2 complexes in the range of the nu1- and nu3-bands of water

The IR spectra of complexes of water with nitrogen molecules in the range of the symmetric (nu(1)) and antisymmetric (nu(3)) bands of H(2)O have been studied in helium droplets. The infrared intensities of the nu(3) and nu(1) modes of H(2)O were found to be larger by factors of 1.3 and 2, respectively, in the N(2)-H(2)O complexes. These factors are smaller than those obtained in recent theoretical calculations. The conformation of the N(2)-H(2)O complex was estimated. Spectra and IR intensities of the (N(2))(2)-H(2)O and N(2)-(H(2)O)(2) complexes were also obtained and their structures are discussed.

Intermolecular potential and second virial coefficient of the water-nitrogen complex

The authors construct a rigid-body (five-dimensional) potential energy surface for the water-nitrogen complex using the systematic intermolecular potential extrapolation routine. The intermolecular potential is then extrapolated to the limit of a complete basis set. An analytic fit of this surface is obtained, and, using this, the global minimum energy is found. The minimum is located in an arrangement in which N2 is near the H atom of H2O, almost collinear with the OH bond. The best estimate of the binding energy is 441 cm-1 (1 cm-1 approximately 1.986 43x10(-23) J). The extrapolated potential is then used to calculate the second cross virial coefficient over a wide temperature range (100-3000 K). These calculated second virial coefficients are generally consistent with experimental data, but for the most part the former have smaller uncertainties.

Vibrational frequencies and infrared intensities of the hydrogen-bonded complexes of nitrous acid with ethers: ab initio and DFT studies

The vibrational spectra of the binary complexes formed by HONO-trans and HONO-cis with dimethyl and diethyl ethers have been investigated using ab initio calculations at the SCF and MP2 levels with 6-311++G(d,p) basis set and B3LYP calculations with 6-31G(d,p) and 6-31+G(d,p) basis sets. Full geometry optimisation was made for the complexes studied. The accuracy of the ab initio calculations have been estimated by comparison between the predicted values of the vibrational characteristics (vibrational frequencies and infrared intensities) and the available experimental data. It was established, that the methods, used in this study are well adapted to the problem under examination. The predicted values with the B3LYP calculations are very near to the results, obtained with 6-311++G(d,p)/MP2. The ab initio and DFT calculations show that the changes in the vibrational characteristics (vibrational frequencies and infrared intensities) upon hydrogen bonding for the hydrogen-bonded complex (CH3)2O...HONO-trans are larger than for the complex (CH3)2O...HONO-cis.

Infrared absorptions of the H2O⋯H2 complex trapped in solid neon

When a sample of neon to which have been added less than 1% each of H(2) and H(2)O is deposited at 4.3 K, the infrared spectrum of the resulting solid includes an absorption by the vibrational fundamental of H(2), which is normally infrared inactive. New absorptions are also associated with the vibrational fundamentals of the H(2)O in the sample. Similar results are obtained for deuterium-enriched samples. The new peaks are assigned to the van der Waals complex of H(2)O with H(2). As has been found in earlier theoretical, gas-phase, and solid-state studies of this and closely related systems, the infrared absorptions arise principally from complexes involving ortho-H(2), for which J=1.

Theoretical study of the structures, stability and vibrational spectra of the nitrous acid complexes with CH4

The structures, stability and vibrational spectra of the binary complexes CH4...HONO-trans and CH4...HONO-cis have been investigated using ab initio calculations at the SCF and MP2 levels with 6-311++G(d,p) basis set and B3LYP calculations with 6-31G(d,p) and 6-31+G(d,p) basis sets. Full geometry optimization was made for the complexes studied. It was established that the complex CH4...HONO-trans is more stable by 0.41 kcal mol(-1) than the complex CH4...HONO-cis. The accuracy of the ab initio calculations have been estimated by comparison between the predicted values of the vibrational characteristics (vibrational frequencies and infrared intensities) and the available experimental data. It was established, that the methods, used in this study are well adapted to the problem under examination. The predicted values with the B3LYP calculations are very near to the results, obtained with 6-311++G(d,p)/MP2. The changes in the vibrational characteristics of methane and trans-, cis-nitrous acid upon formation of the hydrogen bond show that the complexes CH4...HONO-trans and CH4...HONO-cis have geometry in which the OH group interacts with a methane molecule forming a single hydrogen bond. This fact is confirmed by relatively strong perturbation of the OH stretching vibration to lower frequencies and an increase of the infrared intensity of this vibration up to three times upon hydrogen bonding.