Rare Gas Matrices Research Articles

Infrared spectroscopy of SO 2 clusters in rare gas matrices revisited: Assignment of species in Ar matrix

We have observed infrared spectra of the SO 2 clusters in rare gas matrices (Ar, Kr, Xe). The spectral dependence on temperature and concentration led us to the firm assignment of the SO 2 dimer in Kr and Xe, the result of which was used to reassign dimeric vibrational transitions in Ar that have been controversial for more than ten years.

Quantum initial condition sampling for linearized density matrix dynamics: Vibrational pure dephasing of iodine in krypton matrices

This paper reviews the linearized path integral approach for computing time dependent properties of systems that can be approximated using a mixed quantum-classical description. This approach is applied to studying vibrational pure dephasing of ground state molecular iodine in a rare gas matrix. The Feynman-Kleinert optimized harmonic approximation for the full system density operator is used to sample initial conditions for the bath degrees of freedom. This extremely efficient approach is compared to alternative initial condition sampling techniques at low temperatures where classical initial condition sampling yields dephasing rates that are nearly an order of magnitude too slow compared to quantum initial condition sampling and experimental results.

Matrix isolation IR spectroscopic and ab initio studies of C3N− and related species

Coupled cluster calculations were carried out for C(3)N(-), CCNC(-), C(3)N, CCNC, C(3)N(+), and C(3)O. They support the experimental identification of the C(3)N(-) ion by means of matrix isolation infrared (IR) spectroscopy. The anion was generated in electric discharges through the cyanoacetylene isotopomers HC(3) (14)N, HC(3) (15)N, and (2)HC(3)N, trapped in cryogenic rare gas matrices (Ne, Ar, Kr), and detected via its two most intense IR absorption bands, assigned to the nu(1) and nu(2) stretching vibrations. C(3)N(-) appears to be quite a stable anion, with a vertical detachment energy predicted to be as high as 4.42 eV. A large equilibrium electric dipole moment of 3.10 D facilitates the investigation of C(3)N(-) by microwave spectroscopy and radio astronomy. Various structural parameters and spectroscopic properties have been calculated for all tetra-atomic species considered.

Infrared spectra of (HCOOH)2 and (DCOOH)2 in rare gas matrices: A comparative study with gas phase spectra

Infrared absorption spectra of (HCOOH)(2) and (DCOOH)(2) in solid argon, krypton, and xenon matrices have been measured and each fundamental band has been assigned. Spectra in Ar and Kr matrices showed notable splitting in contrast to those in Xe, which suggests a difference in structure of the trapping sites. A comparison with the reported jet-cooled spectra has shown that vibrational structures of the spectra of (HCOOH)(2) and (DCOOH)(2) in the O-H stretching region are preserved in the matrices. On the other hand, the C-O stretching band of (HCOOH)(2) shows a drastic change upon matrix isolation, wherein the Fermi-triad feature observed in gas phase [F. Ito, Chem. Phys. Lett. 447, 202 (2007)] could not be identified. No substantial change of the vibrational structure has been found for matrix-isolated (DCOOH)(2). The differences of the vibrational structures in the matrix-isolation spectra and in the jet-cooled spectra have been qualitatively accounted for using the idea of anharmonic couplings among "matrix-shifted harmonic states."

Photoluminescence of atomic gold and silver particles in soda-lime silicate glasses

We report the chemistry and photophysics of atomic gold and silver particles in inorganicglasses. By synchrotron irradiation of gold-doped soda-lime silicate glasses we could create andidentify unambiguously the gold dimer as a stable and bright luminescing particle embedded inthe glassy matrix. The gold dimer spectra coincide perfectly with rare gas matrix spectra ofAu2. The glass matrix is, however, stable for years, and is hence perfectly suitedfor various applications. If the irradiated gold-doped sample is annealed at550 °C a bright green luminescence can be recognized. Intense 337 nm excitation inducesa decrease of the green luminescence and the reappearance of the 753 nmAu2 emission, indicating a strong interrelationship between both luminescence centers.Time-dependent density functional theory (TD-DFT) calculations indicate that the greenluminescence can be assigned to noble metal dimers bound to silanolate centers. Thesecomplexes are recognized as the first stages in the further cluster growth process, which hasbeen investigated with small-angle x-ray scattering (SAXS). In silver-doped glasses,Ag0 atoms can be identified with electron paramagnetic resonance(EPR) spectroscopy after synchrotron activation. Annealing at300 °C decreases theconcentration of Ag1, but induces an intense white light emission with 337 nm excitation. The white luminescencecan be decomposed into bands that are attributed to small silver clusters such asAg2,Ag3 and Ag4, and an additional band matching the green emission of gold-doped glasses.

Amplified emission of phthalocyanine isolated in cryogenic matrices

Laser induced fluorescence spectroscopy of free-base (H(2)Pc) and zinc (ZnPc) phthalocyanines trapped in rare gas and nitrogen matrices reveals a quite unexpected phenomenon with a moderate increase in the laser intensity. In all matrices except Xe, a huge increase occurs in the intensity of an emission band near 755 nm when pumping the S(1) <-- S(0) transition. The band involves a vibrational mode of the ground state, located at 1550 and 1525 cm(-1) for H(2)Pc and ZnPc, respectively. Many of the characteristics of amplified emission (AE) are exhibited by this vibronic transition. Excitation scans recorded for the AE band yield greatly enhanced site selectivity compared to what is obtained in normal fluorescence excitation scans.

Molecular Structure, Vibrational Spectra, Quantum Chemical Calculations and Photochemistry of Picolinamide and Isonicotinamide Isolated in Cryogenic Inert Matrixes and in the Neat Low-Temperature Solid Phases

Picolinamide (PA) and isonicotinamide (INA), two structural isomers of pyridinecarboxamide, have been investigated by matrix isolation and low-temperature solid-state infrared spectroscopy, combined with UV (lambda > 235 nm) photoexcitation and density functional theory and ab initio (MP2) theoretical studies. In consonance with the theoretical data, both PA and INA were found to exist in a single conformation in cryogenic rare gas matrixes. Comparison between the experimental spectra of the matrix-isolated compounds with those theoretically predicted allowed for full assignment of the experimental spectra. In situ UV (lambda > 235 nm) irradiation of the matrixes showed that only PA reacts, with production of isocyanic acid and pyridine, the first photoproduct further reacting to yield CO + NH and cyanic acid. The different photochemical behavior of the two compounds was explained taking into consideration their different structures. The infrared spectra of (i) the low-temperature glassy state resulting from fast deposition of vapors of the compounds onto a substrate cooled to 10 K, (ii) the crystal resulting from the annealed amorphous film of the compound, and (iii) the room-temperature crystals (alpha-phase) of the studied compounds were also obtained, fully assigned and correlated with intermolecular interactions present in the condensed phases, in particular H-bond interactions, showing that these latter are stronger in INA than in PA.

Shape dynamics during deposit of simple metal clusters on rare-gas matrices

Using a combined quantum-mechanical--classical method, we study the collisions of small Na clusters with large Ar clusters as a model for cluster deposition. We work out basic mechanisms by systematic variation of the collision energy, system sizes, and orientations. The soft Ar material is found to serve as an extremely efficient shock absorber. The collisional energy is quickly transferred at first impact, and the Na clusters are always captured by the Ar surface. The distribution of the collision energy into the Ar system proceeds very fast at the velocity of sound. The relaxation of shapes goes at a slower pace using times of several picoseconds. It produces a substantial rearrangement of the Ar system, while the Na cluster remains rather robust.

Electronic excitations induced by the impact of coinage metal ions and clusters on a rare gas matrix: Neutralization and luminescence

Low-energy collisions of atomic ions and cluster ions with rare gas covered metal substrates can lead to strong light emission which is element and size specific. Instead of a direct energy transfer into the electronic system of the cluster the observed emission originates from excitons trapped in the rare gas layer which carries the excitation energy. The nature of the processes involved in the neutralization and excitation of the neutral clusters electronic system are discussed. Strong analogies to thermoluminescence are found.

Significant increase in the stability of rare gas hydrides on insertion of beryllium atom

Chemical binding between a rare gas atom with other elements leading to the formation of stable chemical compounds has received considerable attention in recent years. With an intention to predict highly stable novel rare gas compounds, the process of insertion of beryllium atom into rare gas hydrides (HRgF with Rg=Ar, Kr, and Xe) has been investigated, which leads to the prediction of HBeRgF species. The structures, energetic, and charge distributions have been obtained using MP2, density functional theory, and CCSD(T) methods. Analogous to the well-known rare gas hydrides, HBeRgF species are found to be metastable in nature; however, the stabilization energy of the newly predicted species has been calculated to be significantly higher than that of HRgF species. Particularly, for HBeArF molecule, it has been found to be an order of magnitude higher. Strong chemical binding between beryllium and rare gas atom has also been found in the HBeArF, HBeKrF, and HBXeF molecules. In fact, the basis set superposition error and zero-point energy corrected Be-Ar bond energy calculated using CCSD(T) method has been found to be 112 kJ/mol, which is the highest bond energy ever achieved for a bond involving an argon atom in any chemically bound neutral species. Vibrational analysis reveals a large blueshift (approximately 200 cm(-1)) of the H-Be stretching frequency in HBeRgF with respect to that in BeH and HBeF species. This feature may be used to characterize these species after their preparation by the laser ablation of Be metal along with the photolysis of HF precursor in a suitable rare gas matrix. An analysis of the nature of interactions involved in the present systems has been performed using theory of atoms in molecules (AIM). Geometric as well as energetic considerations along with the AIM results suggest a substantial covalent nature of Be-Rg bond in these systems. Thus, insertion of a suitable metal atom into rare gas hydrides is a promising way to energetically stabilize the HRgX species, which eventually leads to the formation of a new class of insertion compounds, viz., rare gas metallohydrides.

Embedded metal cluster in strong laser fields

We discuss microscopic mechanisms of the violent dynamics following strong laser excitation of a metal cluster embedded in a rare gas matrix, taking as test case Na 8@Ar 434. This covers at least two aspects: first, it represents the typical experimental situation of metal clusters handled in rare gas matrices or a finite drop of surrounding rare gas material, and second, it serves as a generic test case for highly excited chromophores in inert surroundings addressing questions of energy transport and perturbation of the medium. We simulate the process up to 10 ps using a mixed quantum-mechanical (for the electrons) and classical (ions and atoms) approach and analyze the emerging dynamics with respect to all basic constituents: cluster electrons, cluster ions, and matrix atoms. We find several stages of relaxation taking place with time scales from a few fs to over a few ps and much slower processes remaining for long after the simulation. A particularly interesting aspect is that the surrounding rare gas material stabilizes a highly charged metal cluster which would otherwise explode without delay.

Photochromism in p-methylbenzoylthioacetone and related β-thioxoketones

Irradiation of p-methylbenzoylthioacetone with UV or visible light brings about spectral changes characteristic for the photochromic behavior of β-thioxoketones. The nature of the initial species and of the photochromic product can be assigned based on spectral studies of the electronic and IR spectra in rare gas matrices combined with quantum chemical calculations. Additional arguments for the vibrational assignments are provided by using polarized light to induce the phototransformation, and by subsequent measurements of linear dichroism on partially aligned samples. Comparison with the results previously obtained for three related molecules: thioacetylacetone, p-methyl(thiobenzoyl)acetone, and monothiodibenzoylmethane reveals a common pattern of the photochromic reaction. In all four molecules, the initial species corresponds to an intramolecularly hydrogen-bonded enolic molecular structure, and the main photochromic product to an “open”, nonchelated enethiolic counterpart. On the basis of a computational TD-DFT study of ground and excited electronic states, possible mechanisms of the photochromic transformation are discussed.

Infrared Spectroscopic and Density Functional Theory Study on the Reactions of Rhodium and Cobalt Atoms with Carbon Dioxide in Rare-Gas Matrixes

Reactions of laser-ablated rhodium and cobalt atoms with carbon dioxide molecules in solid argon and neon have been investigated using matrix isolation infrared spectroscopy. The OMCO, O2MCO, OMCO(-) (M = Rh, Co), OCo2CO, and OCoCO(+) molecules have been formed and characterized on the basis of isotopic shifts, mixed isotopic splitting patterns, ultraviolet irradiation, CCl4-doping experiments, and the change of laser power. Density functional theory calculations have been performed on these products. The overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these products from the matrix infrared spectrum.

Intramolecular Hydrogen Atom Tunneling in 2-Chlorobenzoic Acid Studied by Low-Temperature Matrix-Isolation Infrared Spectroscopy

Intramolecular hydrogen atom tunneling in 2-chlorobenzoic acid has been investigated by low-temperature matrix-isolation infrared spectroscopy with the aid of density functional theory calculation. Infrared spectra of two relatively stable syn isomers, SC and ST, were observed in argon and xenon matrixes. When the matrix samples were annealed after deposition, the isomerization from ST to SC occurred around the benzene-carboxyl bond. Two less stable anti isomers, AT, which has an OH...Cl intramolecular hydrogen bond, and AC, which has no OH...Cl bond, were produced from SC and ST upon UV irradiation. When the matrix samples were kept in the dark after UV irradiation, AT and AC changed to ST and SC, respectively, by spontaneous isomerization around the C-O axis in the carboxyl group. The rate constants of isomerization, AT --> ST, in a Xe matrix were estimated from the absorbance changes at various matrix temperatures. The rate constants showed a drastic decrease in deuteration of the hydrogen atom of the carboxyl group. The relationship between the rate constants and the matrix temperature did not follow the Arrhenius law. These findings lead to the conclusion that the isomerization of AT --> ST and AC --> SC in low-temperature rare-gas matrixes proceeds through intramolecular hydrogen atom tunneling.

Structural properties and optical response of Na clusters in Ne, Ar, and Kr matrices

We discuss the structural properties and optical response of a small Na cluster inside rare-gas (RG) matrices of Ne, Ar, or Kr atoms. The mixed systems are described with a hierarchical model, treating the cluster at a quantum-mechanical level and the matrix atoms classically in terms of their positions and polarizations. We pay special attention to the differences caused by the different matrix types. These differences can be explained by the interplay of core repulsion and dipole attraction in the interaction between the cluster electrons and the RG atoms.

Efficient trapping of silver cations in a rare gas matrix: Ag3+ in argon

Mass selected cations of Ag clusters are deposited, together with Ar seeded with CO2 (or other electron scavengers such as O2, N2O, or CCl4), on a cold substrate, while being flooded with low energy electrons. Optical absorption measurements reveal an efficient trapping of Ag cluster cations in the Ar matrix, provided that CO2 or another electron scavenger is present to ensure charge neutrality of the matrix. The spectrum of Ag3+ thus obtained is in excellent agreement with previous predictions from quantum chemical calculations.

S 1 ( A 1 1 ) ← S ( A 1 1 ) transition of benzo[g,h,i]perylene in supersonic jets and rare gas matrices

The study of the S1(1A1)<--S0(1A1) transition of benzo[g,h,i]perylene (BghiP, C22H12) in supersonic jets and solid rare gas matrices is reported. In the jet-cooled spectrum, the origin band position is located at 25,027.1+/-0.2 cm-1, the assignment being supported by the analysis of vibrational shifts and rotational band contours. Except for the origin band, which is weak, all bands are attributed to the fundamental excitation of nontotally symmetric b1 vibrational modes of S1. The intensity pattern is interpreted as a consequence of the weak oscillator strength of the electronic transition combined with intensity-borrowing through vibronic interaction between the S1(1A1) and S2(1B1) states. The spectra of the S1(1A1)<--S0(1A1) and S2(1B1)<--S0(1A1) transitions have also been measured for BghiP in solid neon and argon matrices. The comparison of the redshifts determined for either transition reveals that the polarizability of BghiP is larger in its S2 than in its S1 state. Bandwidths of 2.7 cm-1 measured in supersonic jets, which provide conditions relevant for astrophysics, are similar to those of most diffuse interstellar bands. The electronic transitions of BghiP are found to lie outside the ranges covered by present databases. From the comparison between experimental spectra and theoretical computations, it is concluded that the accuracy of empirical and ab initio approaches in predicting electronic energies is still not sufficient to identify astrophysically interesting candidates for spectroscopic laboratory studies.

Vibrational spectroscopy of interstellar molecules

In this paper we describe how infrared vibrational spectroscopy has been applied in our laboratory to three areas of interest to interstellar chemistry: the origin of the unidentified interstellar infrared emission bands, the depletion of the iron in the interstellar medium, and the fractionation of isotope-bearing molecules in space. In the first area, infrared absorption spectra of polycyclic aromatic hydrocarbons and their ions trapped in cryogenic rare gas matrices have been analyzed and shown to coincide well with the frequencies and relative intensities of the unidentified infrared emission bands. These bands have been observed from many sources in interstellar space, including reflection and planetary nebulae and H II regions, in parts of the Milky Way, as well as other galaxies. In the second area, a free electron laser, with tunable output in the infrared, has been utilized to record resonant multiphoton photodissociation vibrational spectra of various polycyclic aromatic hydrocarbons complexed with Fe+ in a Fourier transform ion cyclotron resonance mass spectrometer. Stable complexes found for Fe+ and a number of PAHs suggest that iron could be sequestered in such species and that they could function as carriers of the unidentified infrared emission bands. In the third area, the photo-induced 13C-isotopic scrambling in the C3 carbon cluster has been investigated by matrix isolation infrared spectroscopy. Fractionation is shown to arise from small zero-point energy differences in the C3 isotopomers. A proposed mechanism of isotopic scrambling involving the formation of cyclic C3 intermediates may be applicable to other species for which isotopic fractionation has also been observed in the ISM.

Theoretical simulation of the six fundamental frequencies of trans-HONO in the gas phase and in rare gas matrices

Five of the six experimental gas-phase fundamental frequencies of trans-HONO (except ν(N O)) are simulated fairly well by anharmonic calculations at B3LYP with the basis set 6-311++(2df,2pd) or 6-311++(3df,3pd). As far as the argon, krypton, and xenon matrix effect on the molecule is concerned, the matrix-induced frequency shifts of the six fundamental modes are simulated reasonably within the framework of polarizable continuum model with integral equation formalism (IEF–PCM) by harmonic calculations at B3LYP with any of the three basis sets 6-311++(df,pd), 6-311++(2df,2pd), and 6-311++(3df,3pd).

Infrared Spectroscopic and Density Functional Theory Study on the Reactions of Lanthanum Atoms with Carbon Dioxide in Rare-Gas Matrices

Reactions of laser-ablated La atoms with CO2 molecules in solid argon and neon have been investigated using matrix-isolation infrared spectroscopy. On the basis of isotopic shifts, mixed isotopic splitting patterns, and CCl4-doping experiments, absorptions at 1839.9 and 753.6 cm-1 in argon and 1855.9 and 771.3 cm-1 in neon are assigned to the C-O and La-O stretching vibrations of the OLaCO molecule, respectively. Ultraviolet-visible photoinduced isomerization of OLaCO to La-(eta2-OC)O and OLa-(eta2-CO) have been observed under different wavelength photolyses in the solid matrix. The neon matrix experiments give the C-O and La-O stretching vibrations of the OLaCO- anion at 1769.5 and 779.3 cm-1, respectively. Density functional theory calculations have been performed on these products, which support the experimental assignments of the infrared spectra. The present study reveals that the C-O stretching vibrational frequencies of OMCO decrease from Sc to La, which indicates an increase in metal d orbital --> CO pi* back-donation in this series.