Solvation of triplet Rydberg states of molecular hydrogen in superfluid helium

We report ab initio interaction potentials, transition dipole moments, and radiative lifetimes for the four lowest triplet states of ${\mathrm{H}}_{2}:$ $b$ ${}^{3}{\ensuremath{\Sigma}}_{u}^{+},$ $c$ ${}^{3}{\ensuremath{\Pi}}_{u},$ $a$ ${}^{3}{\ensuremath{\Sigma}}_{g}^{+},$ and $e$ ${}^{3}{\ensuremath{\Sigma}}_{u}^{+},$ and their response to the perturbation due to approaching ground state He atom. Hybrid density functional\char21{}quantum Monte Carlo calculations employing the ab initio interaction potentials are then used for calculating the liquid structure around the molecular excimers in bulk superfluid ${}^{4}\mathrm{He}.$ Calculations demonstrate a wide variety of possible solvation …

Exploring CO2 hydrogenation to methanol at a CuZn–ZrO2 interface via DFT calculations

Multi-component heterogeneous catalysts are among the top candidates for converting greenhouse gases into valuable compounds. Combinations of Cu, Zn, and ZrO2 (CZZ) have emerged as promisingly efficient catalysts for CO2 hydrogenation to methanol. To explore the catalytic mechanism, density functional theory (DFT) calculations and the energetic span model (ESM) were used to study CO2 conversion routes to methanol on CuZn–ZrO2 interfaces with a varying Zn content. Our results demonstrate that the presence of Zn sites at the interface improves CO2 binding. However, the adsorption and activation energies are insensitive to Zn concentration. The calculations also show that the hydrogenation of …

Raman spectroscopy and crystal-field split rotational states of photoproducts CO and H2 after dissociation of formaldehyde in solid argon.

Raman signal is monitored after 248 nm photodissociation of formaldehyde in solid Ar at temperatures of 9-30 K. Rotational transitions J = 2 ← 0 for para-H(2) fragments and J = 3 ← 1 for ortho-H(2) are observed as sharp peaks at 347.2 cm(-1) and 578.3 cm(-1), respectively, which both are accompanied by a broader shoulder band that shows a split structure. The rovibrational spectrum of CO fragments has transitions at 2136.5 cm(-1), 2138.3 cm(-1), 2139.9 cm(-1), and 2149 cm(-1). To explain the observations, we performed adiabatic rotational potential calculations to simulate the Raman spectrum. The simulations indicate that the splitting of rotational transitions is a site effect, where H(2) …

Time-dependent alignment of molecules trapped in octahedral crystal fields.

The hindered rotational states of molecules confined in crystal fields of octahedral symmetry, and their time-dependent alignment obtained by pulsed nonresonant laser fields, are studied computationally. The control over the molecular axis direction is discussed based on the evolution of the rotational wave packet generated in the cubic crystal-field potential. The alignment degree obtained in a cooperative case, where the alignment field is applied in a favorable crystal-field direction, or in a competitive direction, where the crystal field has a saddle point, is presented. The investigation is divided into two time regimes where the pulse duration is either ultrashort, leading to nonadia…

Rotational coherence imaging and control for CN molecules through time-frequency resolved coherent anti-Stokes Raman scattering

Numerical wave packet simulations are performed for studying coherent anti-Stokes Raman scattering (CARS) for CN radicals. Electronic coherence is created by femtosecond laser pulses between the X²Σ and B²Σ states. Due to the large energy separation of vibrational states, the wave packets are superpositions of rotational states only. This allows for a specially detailed inspection of the second- and third-order coherences by a two-dimensional imaging approach. We present the time-frequency domain images to illustrate the intra- and intermolecular interferences, and discuss the procedure to rationally control and experimentally detect the interferograms in solid Xe environment. peerReviewed

Dynamics behind the long-lived coherences of I2 in solid Xe.

The absorption spectrum of I2 in solid Xe shows resolved zero-phonon lines and phonon side bands near the origin of the B←X transition (550-625 nm). The long-lived |B⟩⟨X| coherence in this energy range (T2 = 600 fs on average) emerges as vibrationally unrelaxed fluorescence in resonance Raman (RR) spectra. Upon excitation in the structureless continuum at 532 nm, the oscillatory RR progression exhibits electronic dephasing time of T2 = 150 fs. Two RR progressions with markedly different vibrational coherence on the X-state are observed. The main progression of sharp overtones (T221 ps) is assigned to molecules trapped in double-substitution sites. The minor progression, which shows dephasin…

Iodine−Benzene Complex as a Candidate for a Real-Time Control of a Bimolecular Reaction. Spectroscopic Studies of the Properties of the 1:1 Complex Isolated in Solid Krypton

The properties of the 1:1 iodine-benzene complex isolated in a solid Kr matrix at low temperatures have been studied using UV-vis absorption, FTIR, resonance Raman, and femtosecond coherent anti-Stokes Raman spectroscopy (fs-CARS). The use of all these techniques on similar samples provides a wide view on the spectroscopic properties of the complex and allows comparison and combination of the results from different methods. The results for the complex cover its structure, the changes in the iodine molecule's vibrational frequencies and electronic absorption spectrum upon complexation, and the dynamics of the complexed I(2) molecule on both ground and excited electronic states. In addition, …

From Monomer to Bulk: Appearance of the Structural Motif of Solid Iodine in Small Clusters

Formation of iodine clusters in a solid krypton matrix was studied using resonance Raman spectroscopy with a 1 cm(-1) resolution. The clusters were produced by annealing of the solid and recognized by appearance of additional spectral transitions. Two distinct regions, red-shifted from the fundamental vibrational wavenumber of the isolated I(2) at 211 cm(-1), were observed in the signal. The intermediate region spans the range 196-208 cm(-1), and the ultimate region consists of two peaks at 181 and 190 cm(-1) nearly identical to crystalline I(2). The experimental results were compared to DFT-D level electronic structure calculations of planar (I(2))(n) clusters (n = 1-7). The dimer, trimer,…

Rotation of methyl radicals in molecular solids.

Electron spin resonance (ESR) measurements were carried out to study the rotation of methyl radicals (CH(3)) in solid carbon monoxide, carbon dioxide, and nitrogen matrices. The radicals were produced by dissociating methane by plasma bursts generated by a focused 193 nm ArF excimer laser radiation during the gas condensation on the substrate. The ESR spectra exhibit anisotropic features that persist over the temperature range examined, and in most cases this indicates a restriction of rotation about the C(2) symmetry axis. A nonrotating CH(3) was also observed in a CO(2) matrix. The intensity ratio between the symmetric (A) and antisymmetric (E) nuclear spin states was recorded as a functi…

Influence of a Cu–zirconia interface structure on CO2 adsorption and activation

CO2 adsorption and activation on a catalyst are key elementary steps for CO2 conversion to various valuable products. In the present computational study, we screened different Cu–ZrO2 interface structures and analyzed the influence of the interface structure on CO2 binding strength using density functional theory calculations. Our results demonstrate that a Cu nanorod favors one position on both tetragonal and monoclinic ZrO2 surfaces, where the bottom Cu atoms are placed close to the lattice oxygens. In agreement with previous calculations, we find that CO2 prefers a bent bidentate configuration at the Cu–ZrO2 interface and the molecule is clearly activated being negatively charged. Strain…

Coherence and control of molecular dynamics in rare gas matrices

Raman spectroscopy and crystal-field split rotational states of photoproducts CO and H2 after dissociation of formaldehyde in solid argon

Raman signal is monitored after 248 nm photodissociation of formaldehyde in solid Ar at temperatures of 9–30 K. Rotational transitions J = 2 ← 0 for para-H2 fragments and J = 3 ← 1 for ortho-H2 are observed as sharp peaks at 347.2 cm−1 and 578.3 cm−1, respectively, which both are accompanied by a broader shoulder band that shows a split structure. The rovibrational spectrum of CO fragments has transitions at 2136.5 cm−1, 2138.3 cm−1, 2139.9 cm−1, and 2149 cm−1. To explain the observations, we performed adiabatic rotational potential calculations to simulate the Raman spectrum. The simulations indicate that the splitting of rotational transitions is a site effect, where H2 molecules can resi…

Ultrafast dynamics of halogens in rare gas solids

We perform time resolved pump-probe spectroscopy on small halogen molecules ClF, Cl2, Br2, and I2 embedded in rare gas solids (RGS). We find that dissociation, angular depolarization, and the decoherence of the molecule is strongly influenced by the cage structure. The well ordered crystalline environment facilitates the modelling of the experimental angular distribution of the molecular axis after the collision with the rare gas cage. The observation of many subsequent vibrational wave packet oscillations allows the construction of anharmonic potentials and indicate a long vibrational coherence time. We control the vibrational wave packet revivals, thereby gaining information about the vib…

Femtosecond coherent anti-Stokes Raman-scattering polarization beat spectroscopy of I2–Xe complex in solid krypton

Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out to study the interaction between xenon atom and iodine molecule in a solid krypton matrix. Interference between the CARS polarizations of the "free" and complexed iodine molecules is observed, while the quantum beats of the complex are not detected due to low concentration. Vibrational analysis based on the polarization beats yields accurate molecular constants for the I2-Xe complex. The harmonic frequency of the I2-Xe complex is found to be redshifted by 0.90 cm-1 when compared to the free I2, whereas the anharmonicity is approximately the same. The dephasing rate of the complex is found to be somewhat …

Influence of a Cu–zirconia interface structure on CO2 adsorption and activation

CO2 adsorption and activation on a catalyst are key elementary steps for CO2 conversion to various valuable products. In the present computational study, we screened different Cu–ZrO2 interface structures and analyzed the influence of the interface structure on CO2 binding strength using density functional theory calculations. Our results demonstrate that a Cu nanorod favors one position on both tetragonal and monoclinic ZrO2 surfaces, where the bottom Cu atoms are placed close to the lattice oxygens. In agreement with previous calculations, we find that CO2 prefers a bent bidentate configuration at the Cu–ZrO2 interface and the molecule is clearly activated being negatively charged. Strain…

Excitation of rotons in parahydrogen crystals: The laser-induced-molecular-alignment mechanism

Solid parahydrogen (p-H₂) is known to support long-lived coherences, of the order of 100 ps, which enables high-resolution spectroscopy in the time domain. Rotational Raman-type excitations to sublevels of J=2 are delocalized due to electric-quadrupole–quadrupole coupling in p-H₂ crystals, and the resulting states can be characterized as rotons. Wave packets of rotons exhibit molecular alignment with respect to laboratory coordinates. Here the concept of field-free molecular alignment, induced by strong ultrashort laser pulses, is extended into a molecular solid case. We derive a solid-state analog for the gas-phase alignment measure and illustrate the time-dependent alignment degree in p-H…

Rotation of methyl radicals in a solid krypton matrix

Electron spin resonance (ESR) measurements were carried out to study the rotation of methyl radicals (CH(3)) in a solid krypton matrix at 17-31 K temperature range. The radicals were produced by dissociating methane by plasma bursts generated by a focused 193 nm excimer laser radiation during the krypton gas condensation on the substrate. The ESR spectrum exhibits only isotropic features at the temperature range examined, and the intensity ratio between the symmetric (A) and antisymmetric (E) spin state lines exhibits weaker temperature dependence than in a solid argon matrix. However, the general appearance of the methyl radical spectrum depends strongly on temperature due to the pronounce…

Addressing Dynamics at Catalytic Heterogeneous Interfaces with DFT-MD: Anomalous Temperature Distributions from Commonly Used Thermostats.

Density functional theory-based molecular dynamics (DFT-MD) has been widely used for studying the chemistry of heterogeneous interfacial systems under operational conditions. We report frequently overlooked errors in thermostated or constant-temperature DFT-MD simulations applied to study (electro)catalytic chemistry. Our results demonstrate that commonly used thermostats such as Nose−Hoover, Berendsen, and simple velocity rescaling methods fail to provide are liable temperature description for systems considered. Instead, nonconstant temperatures and large temperature gradients within the different parts of the system are observed. The errors are not a “feature” of any particular code but …

A fugacity model assessment of ibuprofen, diclofenac, carbamazepine, and their transformation product concentrations in an aquatic environment

An updated version of FATEMOD, a multimedia fugacity model for environmental fate of organic chemicals, was set up to assess environmental behaviour of three pharmaceuticals in northern Lake Päijänne, Finland. Concentrations of ibuprofen, diclofenac, and carbamazepine were estimated at various depths at two sites: near a wastewater treatment plant and 3.5 km downstream the plant. When compared with environmental sampling data from corresponding depths and sites, the predicted concentrations, ranging from nanograms to hundreds of nanograms per litre, were found to be in good agreement. Weather data were utilised with the model to rationalise the effects of various environmental parameters on…

Long-Lived Electronic Coherence of Iodine in the Condensed Phase: Sharp Zero-Phonon Lines in the B↔X Absorption and Emission of I2 in Solid Xe

Our study of B←X absorption of molecular iodine (I2) isolated in a low-temperature crystalline xenon has revealed an exceptionally long-lived electronic coherence in condensed phase conditions. The visible absorption spectrum shows prominent vibronic structure in the form of zero-phonon lines (ZPLs) and phonon side bands (PSBs). The resolved spectrum implies weak interaction of the chromophore to the lattice degrees of freedom. The coherence extends past the vibrational period of the excited state molecule, unlike that observed in any condensed phase environment for I2 so far. The ZP transitions from the relaxing B-state populations were resolved in the hot luminescence when the 532 nm lase…

Vibrational characterization of the 1:1 iodine-benzene complex isolated in solid krypton.

The structure and properties of a 1:1 iodine-benzene complex isolated in an inert krypton matrix at low temperature have been studied with infrared and resonance Raman spectroscopy and with MP2 calculations. The structure of the ground-state complex is found to be unsymmetric, and the I-I vibrational frequency is found to be red-shifted by 3.94 cm(-1) upon complexation. The experimental data agree well with computational results, leading to the conclusion that the I2-Bz complex structure is not axial but of above-bond type, identically with other halogen-benzene complexes.