Matrix Isolation Study Research Articles

Infrared matrix isolation study of the oxidation of H2S by CrCl2O2

The thermal and photochemical reactions between CrO2Cl2 and H2S have been investigated using matrix isolation infrared spectroscopy. Twin-jet co-deposition of the two reagents into argon matrices at 14 K followed by irradiation with light of lambda > 300 nm led to the growth of a number of new bands. These have been assigned to the HSOH-CrCl2O complex, and to SO2. These assignments were supported by deuterium isotopic substitution and high level density functional calculations. Merged-jet deposition with the reaction zone at temperatures above 125 degrees C led to substantial yields of SO2 and HCl, as well as the complex of HCl with excess parent H2S. The evidence suggests that the thermal and photochemical reactions may follow different pathways.

M^|^ouml;ssbauer Investigation into the Reactions of Laser-evaporated Iron with Solid Oxygen at Low Temperatures

Laser-ablation has been studied extensively and has been applied to many fields including the surface treatment of solids and the formation of thin films. Laser-evaporation is a very useful method for vaporizing various kinds of materials without causing radiant heating of surrounding materials. This makes it a convenient method for vaporizing materials near a cold head in a cryostat in order to study low-temperature reactions. We have previously reported reactions of laser-evaporated iron atoms with various reactant gases using a low temperature matrix isolation technique and Mossbauer spectroscopy. 1-4 The reactions of laser-evaporated iron atoms with oxygen produced FeO, Fe(O2), FeO3, (O2)FeO2, and OFeO which are reaction products of the gas phase and are trapped in a low temperature Ar matrix. 5 We have also reported laserdeposition of Fe metal onto Al or Si substrates at various temperatures, 6 and the formation of Fe-Al alloy or Fe-Si compounds was observed at the boundary between the Fe-films and the Al or Si substrate. Laser-deposition of hematite or magnetite onto Al substrates produced iron oxide films whose composition varied depending on the substrate temperature. 7 Thereby laser-deposition has the possibility of producing functional films whose chemical compositions and physical properties can be controlled. Here, we report the reactions of laser-evaporated Fe with solid oxygen at 20 K. While the experimental setup is very similar to that employed in our previous matrix-isolation studies, 5 in this study the Fe atoms and O2 gas are introduced alternately to the cold substrate in order to investigate the reaction of Fe with solid oxygen rather than the gas-phase reactions. This study is also a useful cross reference for the 57 Mn in-beam Mossbauer study of solid oxygen, 8 although the densities of 57 Fe and 57 Mn atoms are very different. Furthermore the reac

Matrix Isolation Study of the Reactions of CrO2Cl2 with a Series of Silanes

The reactions between CrO2Cl2 and a series of silanes have been investigated using matrix isolation infrared spectroscopy. Twin-jet codeposition of the two reagents into argon matrices at 14 K followed by irradiation with light of lambda > 300 nm led to the growth of a number of new bands. These have been assigned to the appropriate silanol species formed by oxygen insertion into the Si-H bond, strongly complexed to CrCl2O. The structures and vibrational frequencies of these complexes have been characterized by high-level theoretical calculations. These calculations also support the relative preference for the insertion reaction compared to other possible pathways. Merged-jet codeposition of SiH2Cl2 with CrO2Cl2 at 200 degrees C also led to the formation of the free silanol, HSiCl2OH.

A matrix isolation study of the reactions of OVCl 3 with a series of silanes

The reactions between OVCl 3 and a series of silanes have been investigated using matrix isolation infrared spectroscopy. Twin-jet co-deposition of the two reagents into argon matrices at 14 K followed by irradiation with light of λ>300 nm led to the growth of a number of new bands. These have been assigned to the appropriate silanol species formed by oxygen insertion into the Si–H bond, complexed to VCl 3. The structures and vibrational frequencies of these complexes have been characterized by high-level theoretical calculations. These calculations also support the relative preference for the insertion reaction compared to other possible pathways.

Absorption Spectra of Ground-State and Low-Lying Electronic States of Copper Nitrosyl: A Rare Gas Matrix Isolation Study

The reaction of ground-state Cu atoms with NO during condensation in solid argon, neon, and binary argon/neon mixtures has been reinvestigated. In addition to the ground-state already characterized in rare gas matrixes by its nu1 mode in reactions of laser-ablated Cu with nitric oxide, another very low lying electronic state is observed for CuNO in solid argon. Photoconversion and equilibrium processes are observed between the two lowest lying electronic states following photoexcitations to second and third excited states in the visible and near-infrared. The electronic spectrum of the CuNO complex was also recorded to understand the photoconversion processes. In solid neon, only the ground state (probably 1A') and the second and third excited states are observed. This suggests that interaction with the argon cage stabilizes the triplet state to make 1A' and 3A' ' states almost isoenergetic in solid argon. On the basis of previous predictions founded on DFT calculations on the very low lying 1A' and 3A' ', a mechanism is proposed, involving the singlet-triplet state manifolds. For these two lower and one higher electronic states, 14N/15N, 16O/18O, and 63Cu/65Cu isotopic data on nu1, nu2, and nu3 have been measured. On the basis of harmonic force-field calculations and relative intensities in the vibronic progressions, some structural parameters are estimated. The molecule is bent in all electronic states, with Cu-N-O bond angles varying slightly around 130 +/- 10 degrees , but the Cu-N bond force constants are substantially different, denoting larger differences in bond lengths.

Experimental Matrix Isolation Study and Quantum-Mechanics-Based Normal-Coordinate Analysis of the Anharmonic Infrared Spectrum of Picolinic Acid N-Oxide

This work is, according to our knowledge, the first experimental matrix isolation study of a molecular system with a very short and strong intramolecular OH...O hydrogen bond. It also includes a satisfying interpretation of its entire infrared spectrum. The interpretation relies on the calculation at the DFT/B3LYP/6-31G(d,p) level of the harmonic spectrum and of the anharmonic relaxed potential energy for the stretching motion of the hydrogen-bonded proton, used with our recently modified quantum-mechanics-based normal-coordinate analysis. An important observation about the anharmonic spectrum obtained from this procedure is that the OH stretch coordinate contributes to several normal modes, mixing extensively with other in-plane internal coordinates, in particular OH-bending and C=O-stretching. The two intense normal modes with the largest contributions from the OH-stretching coordinate to the potential energy distribution and to the intensity are located near 1700 and 1500 cm(-1). A calculated anharmonic spectrum obtained from this procedure agrees with the experimental spectrum (frequencies and intensity distribution), within the limits of the estimated uncertainties for the calculation and experiment, allowing the interpretation of the latter. The agreement for the frequencies is about 1-3%. The anharmonic spectrum calculated using the anharmonic keyword in Gaussian 03w is not in satisfactory agreement with experiment insofar as the OH-stretching mode is concerned.

Aggregation of acetic and propionic acid in argon matrices—A matrix isolation and computational study

Monomeric acetic acid M A and propionic acid M P were isolated in argon matrices at 10 K by using a pulse deposition technique. The dimerization of the monomers was induced by warming the matrices from 10 to 40 K. Under these conditions the diffusion of small trapped molecules is rapid and the dimerization could be monitored directly by IR spectroscopy. Both carboxylic acids form the symmetrical dimers B with two strong C O⋯HO hydrogen bridges as the thermodynamically most stable dimers. With acetic acid a less stable dimer A A could be obtained if high concentrations of acetic acid in argon were used during the deposition of the matrix. On annealing this dimer rearranges to the more stable B A . In contrast, propionic acid does not form a corresponding less stable dimer under any experimental condition. These observations are rationalized on the basis of DFT and ab initio calculations.

Matrix Isolation and Density Functional Theory Study of Bis(trifluoromethyl)dioxodiazine: A Photodimer of Trifluoronitrosomethane

Trifluoronitrosomethane (CF3NO) was trapped in rare gas matrixes and irradiated at 633 and 670 nm. The infrared spectra of the postirradiation samples exhibit features consistent with cis and trans conformers of bis(trifluoromethyl)dioxodiazine, a previously uncharacterized species. The concentration dependence of the formation of the dimer is consistent with a mechanism in which monomers trapped in adjacent sites undergo excitation and subsequent reaction. The dimers reversibly form the monomer when irradiated with ultraviolet light. Density functional theory was used to determine the structure of the dimers and predict their infrared and Raman spectra. The predicted vibrational frequencies are in agreement with those observed. A third (skewed) conformation was predicted to have a triplet ground state, but no evidence of this species was observed. All three dimers exhibit significant diradical character, as evidenced by comparatively low N-N and high N-O stretching frequencies. Transition-state calculations predict the dimerization barrier to range from 17.1 (cis) to 35.0 (trans) kJ mol(-1) for the singlet dimers and to be 62.1 kJ mol(-1) for the triplet dimer. This is an example of nitroso dimerization that requires electronic excitation to proceed.

Ab Initio Prediction of the Potential Energy Surface and Vibrational−Rotational Energy Levels of Calcium Dihydride, CaH2

The equilibrium structure and potential energy surface of calcium dihydride, CaH(2), have been determined from large-scale ab initio calculations using the coupled-cluster method, CCSD(T), in conjunction with basis sets of quadruple- and quintuple-zeta quality. The CaH(2) molecule was found to be quasilinear. The HCaH bending potential function was predicted to be extraordinarily flat near the minimum, located at the HCaH angle of 164 degrees. The barrier to linearity was calculated to be just 6 cm(-1). The vibrational-rotational energy levels of various isotopomers were predicted using the variational method. The calculated vibrational fundamental frequencies are in good agreement with the results of matrix-isolation studies, and the other predicted spectroscopic constants can assist in the future detection of calcium dihydride in the gas phase.

Noncovalent Complexes between Dimethyl Ether and Formic Acid—An Ab Initio and Matrix Isolation Study

The complexes formed by noncovalent interactions between formic acid and dimethyl ether are investigated by ab initio methods and characterized by matrix isolation spectroscopy. Six complexes with binding energies between -2.26 and -7.97 kcal mol(-1) (MP2/cc-pVTZ+zero point vibrational energy+basis set superposition erros) are identified. The two strongest bound complexes are, within a range of 0.3 kcal mol(-1), isoenergetic. The binding in these six dimers can be described in terms of OH...O, C=O...H, C-O...H and CH...O interactions. Matrix isolation spectroscopy allowed to characterize the two strongest bound complexes by their infrared spectra.

Interaction of bihalogen anions with nitrogen: Matrix-isolation study and first principle calculations of the (ClHCl) −⋯N 2 and (BrHBr) −⋯N 2 complexes

The N 2 complexes of (ClHCl) − and (BrHBr) − are studied both experimentally using IR absorption spectroscopy and computationally. Two computational [MP2(full)/6-311++G(2d,2p)] geometries for the systems were found, and the cross-like structure is energetically the more stable for both of the systems. The BSSE-corrected interaction energies for the cross-like structures are −500 to −600 cm −1. The matrix-isolation experiments support the formation of this complex structure, and the experimental complexation-induced shift is +4.8 and +7.1 cm −1 for the (ClHCl) −⋯N 2 and (BrHBr) −⋯N 2 complexes, respectively. The HArCl and HKrBr molecules do not appear upon annealing of the photolyzed HCl/Ar and HBr/Kr matrices probably suggesting instability of these molecules.

A matrix isolation study of the photochemically induced reactions of nitrogen dioxide with 1,2-dibromoethene and 1,2-dichloroethene using Fourier transform infrared spectroscopy

Photolyses of matrices of either BrCH CHBr/NO 2/Ar or ClCH CHCl/NO 2/Ar using quartz-filtered radiation ( λ > 240 nm) led to the appearance of infrared bands attributable to carbonyl, carbon monoxide, and ketene species; no bands belonging to a precursor complex NO 2⋯XCH CHX (where X = Br or Cl) were observed upon matrix deposition. The possible reaction pathway is discussed.

Matrix isolation and theoretical study of the photochemical reaction of CH 3CN with CrO 2Cl 2 and OVCl 3

The matrix isolation technique has been combined with theoretical calculations to identify and characterize the photoproducts in the reactions of CH 3CN with CrCl 2O 2 and OVCl 3. Twin jet co-deposition of these reagents led to the formation of a 1:1 molecular complex which was observed using UV/visible spectroscopy. Irradiation of these matrices with light of λ>300 nm led to the observation of new bands in the infrared spectra, the most intense of which was seen at 1942 cm −1 for the CrCl 2O 2/CH 3CN system. The product bands are assigned to the 2η complexes of acetonitrile n-oxide with CrCl 2O and VCl 3, respectively. Identification of these species was supported by extensive isotopic labeling ( 2H and 15N), as well as by B3LYP/6-311++G(d,2p) density functional calculations.

Computational Investigation of the Weakly Bound Dimers HOX···SO3 (X = F, Cl, Br)

The electronic structure and thermochemical stability of the HOX-SO(3) (X = F, Cl, Br) complexes is studied using second-order Møller-Plesset perturbation theory (MP2). The calculated dissociation energies of the HOF-SO(3), HOCl-SO(3), and HOBr-SO(3) complexes are 5.43, 6.02, and 5.98 kcal mol(-1) at MP2/6-311++G(3df,3pd) level, respectively. Anharmonic OH stretching frequencies of the HOX (X = F, Cl, Br) moieties along with the frequency shifts upon complex formation are calculated at the MP2/6-311++G(2df,2p) level. AIM and NBO analyses were also performed. Theoretical data strongly encourage performing of matrix-isolation studies of the title complexes and their spectroscopic identification.

Matrix-isolation and computational study of salicylhydroxamic acid and its photochemical degradation

The IR absorption spectrum of salicylhydroxamic acid (sha) isolated in an argon matrix at 12-21 K has been recorded. Calculations of all the possible entgegen and zusammen keto conformers of sha have been performed at the B3LYP/6-311++G(d,p) level of theory. The computed energies, optimized structures, and relative abundances show that sha exists in the matrix as the z,z,z,z-conformer [relative to the C-O(-H), C-C(-N), C-N and N-O bonds, respectively] and is stabilized by two intramolecular H-bonds. Photofragmentation of the compound in matrix and methanol-water solution has been obtained by irradiation with visible and ultraviolet light. o-Hydroxyphenylisocyanate is the main photolysis product in an argon matrix, while salicylamide is the primary photolysis product in methanol-water solution.

Dimerization of the keto tautomer of acetohydroxamic acid—infrared matrix isolation and theoretical study

Dimerization of the keto tautomer of acetohydroxamic acid has been studied using FTIR matrix isolation spectroscopy and DFT(B3LYP)/6-31+G(d,p) calculations. Analysis of CH 3CONHOH/Ar matrix spectra indicates formation of two dimers in which two intramolecular CO···H ON bonds within two interacting acetohydroxamic acid molecules are retained. A chain dimer I is stabilized by the intermolecular CO···H N hydrogen bond, whereas the cyclic dimer II is stabilized by two intermolecular N H···O(H)N bonds. Twelve vibrations were identified for dimer I and six vibrations for dimer II; the observed frequency shifts show a good agreement with the calculated ones for the structures I and II. Both dimers have comparable binding energies ( Δ E ZPE CP I, II = −7.02, −6.34 kcal mol −1) being less stable than calculated structures III and IV ( Δ E ZPE CP III, IV = −9.50, −8.87 kcal mol −1) in which one or two intramolecular hydrogen bonds are disrupted. In the most stable 10-membered cyclic dimer III, two intermolecular CO···H ON hydrogen bonds are formed at expense of intramolecular hydrogen bonds of the same type. The formation of the less stable (AHA) 2 dimers in the studied matrixes indicates that the formation of (AHA) 2 is kinetically and not thermodynamically controlled.

Reactivity of Atomic Cobalt with Molecular Oxygen: A Combined IR Matrix Isolation and Theoretical Study of the Formation and Structure of CoO2

The reactivity of atomic cobalt toward molecular oxygen in rare gas matrices has been reinvestigated. Experiments confirm that Co atoms in their a(4)F ground state are inert toward O(2) in solid argon and neon but reactive in the b(4)F first excited state, in agreement with the previous gas-phase study of Honma and co-workers. The formation of CoO(2) starting from effusive beams of Co and O(2) has been followed by IR absorption spectroscopy, both in neon and argon matrices. Our observations show that only the dioxo form, OCoO, is stabilized in the matrix and that IR absorptions previously assigned to the peroxo and superoxo forms are due to other, larger species. The present data strongly support the linear geometry in rare gas matrices proposed by Weltner and co-workers. We report on measurements on all IR-active fundamental modes for (16)OCo(16)O, (18)OCo(18)O, and (16)OCo(18)O with additional combination transitions supplying anharmonicity correction. This allows for a 5.93 +/- 0.02 mdyne/A CoO harmonic bond force constant in solid neon. Using the empirical relationship previously optimized for the CoO diatomics, an approximate value for the CoO internuclear bond distance is proposed (1.615 +/- 0.01A). In light of recent theoretical studies predicting (2)A(1) or (6)A(1) electronic ground states, the geometry and electronic structure of the OCoO molecule has also been reconsidered. Calculations carried out at the CCSD(T)/6-311G(3df) level indicate a linear structure with an r(e) = 1.62 A bond distance, consistent with the experimental estimate. For later studies of larger systems, where CCSD(T) calculations become too time-consuming, an effective DFT-based method is proposed which reproduces the basic electronic and geometrical properties of cobalt dioxide. Quantitative results are compared to the experimental data and high-level results regarding bond length and frequencies. This DFT method is used to propose a reaction pathway.

Characterization of Ground and Low-Lying Excited States of CoO4: A Combined Matrix Isolation and DFT Study

The nature of the reaction products between CoO(2) and molecular O(2), isolated in rare gas matrices, have been investigated using IR absorption spectroscopy. In this paper, we report on the vibrational spectrum of the CoO(4) molecule in its ground and first low-lying excited states. Isotopic substitutions using (16)O(2) and (18)O(2) precursors, as well as (16)O(2) + (18)O(2) and (16)O(2) +( 16)O(18)O + (18)O(2) mixtures in either excess argon or neon, enable demonstration of C(2)(v)() and C(s)() structures for the respective states. CoO(4) is formed following molecular diffusion by complexation of ground-state CoO(2) by an O(2) molecule. The molecule is first formed in the excited state and then spontaneously relaxes to the ground state after remaining in the dark. The kinetics of relaxation can be fitted to a first-order exponential decay with an excited-state lifetime estimated around 23 +/- 2 min in argon and 15 +/- 2 min in neon, indicative of a slow, spin-forbidden process. Population of the excited state is induced by photons around 4250 +/- 250 cm(-1). Experimental results are compared to density functional theory (DFT) calculations at the BPW91/6-311G(3df) level. Electronic and geometrical optimizations were carried out starting from the ground-state precursors (i.e., (3)Sigma(g)(-) for O(2) and (2)Sigma(g)(+) for CoO(2)). Calculations predict a (2)A(2) (C(2)(v)()) ground state and a (4)A' (C(s)()) first excited state 0.37 eV above, close to the 4250 +/- 250 cm(-1) experimental excitation energy. The transition pathway is found to involve two supplementary states with crossed potential energy surfaces (PESs): a (2)B(1) excited state, 0.48 eV above the ground state, reached first through an adiabatic transition with a photon around 4800 cm(-1), and a (4)B(1) transition state into which the system relaxes before finally attaining the (4)A' (C(s)()) excited state. Harmonic frequencies and absolute intensities are also calculated and compared with the experimental data, indicating however that the DFT underestimates the internuclear distances for both configurations. Force and interaction constants were obtained with a semiempirical harmonic force-field potential calculation. They were then used in an empirical rule of plot linking force constants and internuclear distances in order to obtain an estimate of the Co-O bond lengths for each state and are compared to the DFT predictions.

Vibrational and Electronic Spectra of Neutral and Ionic Combustion Reaction Intermediates Trapped in Rare‐Gas Matrixes

AbstractFor Abstract see ChemInform Abstract in Full Text.

A matrix isolation and ab initio study of the hydrogen bonded complexes of acetylene with pyridine

Hydrogen bonded complexes of acetylene and pyridine were studied using matrix isolation spectroscopy and ab initio computations. The adduct was formed by depositing acetylene and pyridine in an argon matrix and a 1:1 C 2H 2–NC 5H 5 complex was identified using infrared spectroscopy. Formation of the adduct was evidenced from the shifts in the vibrational frequencies of C 2H 2 in the complex compared with that of free C 2H 2. The molecular structure, vibrational frequencies and stabilization energies of the complex were computed at the HF/6-31++G** and B3LYP/6-31++G** levels. We located one minimum on the potential surface, corresponding to a strongly bound C 2H 2–NC 5H 5 n–σ complex. Both experimental and computational data indicated that C 2H 2 acts as a proton donor and C 5H 5N as a proton acceptor.