Matrix Isolation FTIR Research Articles

Matrix isolation study of the early intermediates in the ozonolysis of selected vinyl ethers

The Criegee mechanism of the ozonolysis reaction of vinyl ethers has been observed by matrix isolation FTIR spectroscopy.

New aspects of UV photolysis of hydrogen peroxide. Nitrogen matrix isolation FTIR and theoretical studies

Abstract UV photochemistry of H 2 O 2 isolated in solid nitrogen at 15 K has been studied experimentally by FTIR matrix isolation technique and theoretically using DFT and MP2 methods. The major photoproducts were identified as (i) nitrous oxide and N 2 O⋯H 2 O complex and (ii) free and complexed to N 2 O hydroxyl radicals. Except for the OH radicals all observed species are unique and characteristic for H 2 O 2 photolysis in solid nitrogen. The identities of the products have been confirmed by comparison with results of quantum chemical calculations, and reference to the spectral data of related molecules. Differences in the photolysis course upon irradiation at 230 and 212 nm are discussed.

Theoretical DFT and matrix isolation FTIR studies of 2-(1,2,4-triazolyl)phenol isomers

The structure, isomerization pathways and vibrational spectra of the important heterocyclic 2-(1,2,4-triazolyl)phenol molecule were investigated by DFT calculations and matrix isolation FTIR spectroscopy. Among forty-five minima located on PES three isomers with intramolecular hydrogen bond OH⋯N, 2-TRP1, 1-TRP1 and 1-TRP2, are the most stable forms with the calculated abundance of 83.4%, 10.3% and 6.0%, respectively. The presented FTIR results allow identification and characterization of these species. Several hydrogen bond parameters such as OH bond distance, νOH wavenumber shift and occupancy of the antibonding σ∗(OH) orbital were found to be linearly related with the estimated interaction energy.

H-Bonding of Sulfuric Acid with Its Decomposition Products: An Infrared Matrix Isolation and Computational Study of the H2SO4·H2O·SO3 Complex

The FTIR matrix isolation spectra of H2SO4 vapors show a group of bands with synchronous growth of their relative intensities which is independent of the water species content of the matrix layer. Their frequency positions indicate that the species they represent is H-bonded and composed of all three components (H2SO4, H2O, and SO3) involved in the vapor decomposition equilibrium of the acid molecule. Structure, stabilization energies, and vibrational frequencies of several H-bonded complexes between these components were considered in B3LYP calculations employing Dunning's correlation-consistent aug-cc-pVTZ basis sets. Correlations between spectral shifts, bond lengths, and H-bond energies were also considered. The best fitting complex is a ring structured 1:1:1 H2SO4·H2O·SO3. The indications are that the complex is formed in the vapor phase and not after deposition. The atmospheric significance may be in its ability to serve as a H-bonding nucleation center even without the presence of additional contaminants.

N-Hydroxyurea dimers: A matrix isolation and theoretical study

The dimerization of N-hydroxyurea (NH2CONHOH) has been investigated by FTIR matrix isolation spectroscopy and DFT(B3LYP)/6-311++G(2d,2p) calculations. The analysis of NH2CONHOH/Ar matrix spectra and comparison with theoretical ones reveal the formation of two types of dimers with a strong OH⋯O hydrogen bond. There is an additional weak interaction between the oxygen atom of the OH group of the proton donor molecule and the NH or NH2 group of the proton acceptor in both dimers, respectively. The identified structures correspond to local minima on the PES. The formation of the less stable structures not the most stable ones indicates that the creation of N-hydroxyurea dimers is related to the dipole-dipole interaction at the initial stage of the dimerization process, which favours generation of polar dimers.

Reactions of Group V Metal Atoms with Hydrogen Sulfide: Argon Matrix Infrared Spectra and Theoretical Calculations

The reaction of laser-ablated vanadium, niobium and tantalum atoms with hydrogen sulfide has been investigated using matrix isolation FTIR and theoretical calculations. The metal atoms inserted into the H−S bond of H2S to form the HMSH molecules (M=V, Nb, Ta), which rearranged to H2MS molecules on annealing for Nb and Ta. The HMSH molecule can also further react with another H2S to form the H2M(SH)2 molecules. These new molecules were identified on the basis of the D2S and H234S isotopic substitutions. DFT (B3LYP and BPW91) theoretical calculations are used to predict energies, geometries, and vibrational frequencies for these novel metal dihydrido complexes and molecules. Reaction mechanism for formation of group V dihydrido complex was investigated by DFT internal reaction coordinate calculations. The dissociation of HVSH gave VS+H2 on broad band irradiation and reverse reaction happened on annealing. Based on B3LYP calculation releasing hydrogen from HVSH is endothermic only by 13.5 kcal/mol with lower energy barrier of 16.9 kcal/mol.

Donor-Acceptor Complexes between Ammonia and Sulfur Trioxide: An FTIR and Computational Study.

The complexes of ammonia with sulfur trioxide have been studied using FTIR matrix isolation spectroscopy and DFT/B3LYP calculations with the aug-cc-pVTZ basis set. The NH3/SO3/Ar matrixes were prepared in two different ways. In one set of experiments the matrix was prepared by the simultaneous deposition of the NH3/Ar mixture and SO3 vapor from the thermal decomposition of K2S2O7. In the second set of experiments thermolysis products of sulfamic acid were trapped in an argon matrix. Both methods of matrix preparation led to the formation of the H3N·SO3 electron donor-acceptor complex that was characterized earlier. In the matrixes comprising thermolysis products of sulfamic acid, in addition to H3N·SO3, the H3N-SO3···NH3 complex (II(D)) was also identified. The identity of the complex was confirmed by comparison of the experimental and theoretical spectra of H3N-SO3···NH3 and D3N-SO3···ND3. The performed calculations show that in H3N-SO3···NH3 the two N atoms and the S atom are collinear; the two S-N bonds are nonequivalent, one is much shorter (2.230 Å) than the other one (2.852 Å). In the AIM topological analysis, the interaction energy decomposition and topological properties of the electron localizability indicator (ELI-D) allowed us to categorize the stronger N-S bond in the II(D) complex as a dative bond and to assume that the fragile N-S bond is a consequence of a weak electron-donor-acceptor interaction. The calculations indicate that the identified II(D) complex corresponds to a local minimum on the PES of the NH3/SO3 system of 2:1 stoichiometry. The (NH3)2SO3 complex, II(HB), corresponding to a global minimum is 7.95 kcal mol(-1) more stable than the II(D) complex. The reason that the II(D) complex is present in the matrix but not the II(HB) complex is discussed.

Conformational composition and population analysis of β-alanine isolated in solid parahydrogen

The conformational composition and the change in conformational ratio induced by UV irradiation of β-alanine have been investigated using solid parahydrogen FT-IR matrix isolation spectroscopy for the first time. In order to assign the observed spectra, the vibrational wavenumbers and intensities of the eleven lowest energy β-alanine conformers were calculated at the B3LYP/aug-cc-pVTZ level of theory. In-situ UV photo-irradiation of β-alanine in solid parahydrogen was used to assist the spectral assignment. Out of the eleven lowest energy conformers, conformers I, II, III, IV, and VII were identified in the solid parahydrogen matrix, with conformer III observed in a matrix environment for the first time. Argon matrix FT-IR spectra of β-alanine were also recorded for comparison and only four conformers, conformers I, II, IV and VII, were found, as reported previously. Conformational changes to higher energy structures were observed when β-alanine was irradiated with UV radiation. These changes were more pronounced in parahydrogen matrices than in argon matrices, indicating the usefulness of solid parahydrogen matrix isolation spectroscopy for the conformational study of amino acids.

Structure and photochemistry of a saccharyl thiotetrazole.

The molecular structure and photochemistry of 5-thiosaccharyl-1-methyltetrazole (TSMT) were studied by means of matrix-isolation FTIR spectroscopy, X-ray crystallography, and theoretical calculations. The calculations predicted two conformers of TSMT that differ in energy by more than 15 kJ mol(-1). The infrared spectrum of TSMT isolated in solid argon was fully assigned on the basis of the spectrum calculated (O3LYP/6-311++G(3df,3pd)) for the most stable conformer. In the crystal, TSMT molecules were found to assume the same conformation as for the isolated molecule, with each molecule forming four hydrogen bonds with three neighboring molecules, leading to a network of TSMT oligomers. Upon UV (λ = 265 nm) irradiation of the matrix-isolated TSMT, two photodegradation pathways were observed, both arising from cleavage of the tetrazolyl ring. Pathway a involves cleavage of the N1-N2 and N3-N4 bonds with extrusion of N2, leading to photostable diazirine and thiocarbodiimide derivatives. The photostability of the photoproduced diazirine under the conditions used precluded its rearrangement to the nitrile imine, as reported for 5-phenyltetrazole by Bégué et al. ( J. Am. Chem. Soc. 2012 , 134 , 5339 ). Pathway b involves cleavage of the C5-N1 and N4-N3 bonds, leading to a thiocyanate and methyl azide, the latter undergoing subsequent fragmentation to give CNH.

Isomers of the acetic acid-water complex trapped in an argon matrix.

The complexes of acetic acid (AcOH) with water have been studied using FTIR matrix isolation spectroscopy and DFT/B3LYP, DFT/B3LYP-D, and MP2 calculations with the aug-cc-pVTZ basis set. The AcOH/H2O/Ar matrices were prepared in two different ways. In one set of experiments, the vapor above a solid AcOH sample, cooled to 203 K, was diluted with H2O/Ar mixture in the vacuum chamber of the cryostat, and the mixture was solidified on the target. In the second set of experiments, the matrix was prepared by simultaneous deposition of AcOH/Ar and H2O/Ar mixtures at room temperature. The first method of matrix preparation strongly favors the formation of the "acyclic" higher energy AcOH-H2O complex I(B) compared to the second one. Warming of matrices containing the higher energy complex, I(B), from 11 to 39 K, results in the decrease of I(B) concentration and formation of the lowest energy cyclic complex I(A). The calculations indicate that I(B) is formed by an O-H···O hydrogen bond between the carbonyl oxygen and a water O-H group and, additionally, by a weak interaction between one of the methyl group hydrogen atoms and the water oxygen atom. The cyclic complex I(A) has a six-membered ring involving two O-H···O bonds. An activation energy of 0.94, 1.71, and 1.38 kcal mol(-1) was calculated for the I(B) → I(A) rearrangement at the B3LYP, B3LYP-D, and MP2 levels of theory, respectively. Van't Hoff plots for the association of H2O and AcOH leading to formation of the complexes I(A) and I(B) are presented and discussed. Evidence is also given for the formation of the AcOH-(H2O)2 and (AcOH)2-H2O complexes in the matrices. A potential atmospheric impact of the enhanced formation of the higher energy I(B) complex at low temperatures is discussed.

Hydrogen bonding in the sulfuric acid-methanol-water system: a matrix isolation and computational study.

Frozen core MP2 and DFT computations were carried out on possible configurations of 1:1 H2SO4·CH3OH and 1:1:1 H2SO4·CH3OH·H2O complexes. Minimum energy structures, stabilization energies, H-bond lengths and vibrational frequencies were calculated. The latter complex can exist in either sequential "linear" configurations involving four H-bonds or "cyclic" structures involving three H-bonds only. However, there is little difference in the energy of stabilization between these two possible forms, indicating a "cooperative effect" between the H-bonds in the latter. This effect is also evidenced by the calculated H-bond lengths. In the cyclic complex, the hydroxyl of either CH3OH or H2O may be the proton donor to the H-bond between them. Argon matrix isolation FTIR spectra of layers with various concentration ratios were recorded. In the hydroxyl stretch wavenumber regions several weak new bands were observed. Their position was found to fit best the cyclic structures. The observed red shifts exceed the corresponding calculated values. Together with the considerable observed bandwidths they are further manifestations of the cooperative effect between the H-bonds. The lower skeletal mode wavenumber regions show a number of sharper bands compatible with those previously reported for dimethyl sulfate and hydrogen methyl sulfate, indicating their formation in the vapor mixing region or at the solid matrix layer interface.

Crystal structure, matrix-isolation FTIR, and UV-induced conformational isomerization of 3-quinolinecarboxaldehyde.

The crystal structure of 3-quinolinecarboxaldehyde (3QC) has been solved, and the compound has been shown to crystallize in the space group P21/c (monoclinic) with a = 6.306(4), b = 18.551(11), c = 6.999(4) Å, β = 106.111(13)°, and Z = 4. The crystals were found to exhibit pseudomerohedral twinning with a twin law corresponding to a two-fold rotation around the monoclinic (100) reciprocal lattice axis (or [4 0 1] in direct space). Individual molecules adopt the syn conformation in the crystal, with the oxygen atom of the aldehyde substituent directed toward the same side of the ring nitrogen atom. In the gas phase, the compound exists in two nearly isoenergetic conformers (syn and anti), which could be successfully trapped in solid argon at 10 K, and their infrared spectra are registered and interpreted. Upon in situ irradiation of matrix-isolated 3QC with UV light (λ > 315 nm), significant reduction of the population of the less stable anti conformer was observed, while that of the conformational ground state (syn conformer) increased, indicating occurrence of the anti → syn isomerization. Upon irradiation at higher energy (λ > 235 nm), the syn → anti reverse photoreaction was observed. Interpretation of the structural, spectroscopic, and photochemical experimental data received support from quantum chemical theoretical results obtained at both DFT/B3LYP (including TD-DFT investigation of excited states) and MP2 levels, using the 6-311++G(d,p) basis set.

Conformational isomerism of pyridoxal. Infrared matrix isolation and theoretical studies

A combined matrix isolation FTIR and theoretical DFT/B3LYP/6–311++G(2p,2d) study of pyridoxal was performed. The calculations resulted in five stable PLHB conformers stabilized by intramolecular OH⋯O bonding between phenolic OH and carbonyl CO groups and another thirteen conformers in which OH or/and aldehyde groups are rotated by 180° around CO or/and CC bonds leading, respectively, to formation of PLO, PLA and PLOA conformers. The analysis of the spectra of the as-deposited matrix indicated that two most stable PLHB1 and PLHB2 conformers with intramolecular hydrogen bond are present in the matrix. The exposure of the PL/Ar matrix to mercury lamp radiation (λ>345nm) induced conformational change of PLHB isomers to PLOA ones.

Carboxylic Group and Its Tetrazolyl Isostere in One Molecule. Matrix Isolation FTIR and DFT Studies on Thermal Decomposition and Photochemistry of (Tetrazol-5-yl)acetic Acid

The title compound (tetrazol-5-yl)acetic acid (TA) is an interesting molecule that contains both a carboxylic group and its isostere tetrazolyl group. Out of nine theoretically predicted stable structures of TA, three appeared to be present in solid argon. Thermal decomposition of the species aided by water molecules was studied in detail both experimentally using FTIR matrix isolation technique and theoretically at the B3LYP/6-311++G(2d,2p) level. Experimentally, it was found that the decarboxylation process appeared at the presence of water traces in the system. Theoretically, it was shown that the energy barrier of the water assisted process was lower by ca. 30 kJ mol(-1) comparing to the process without water participation. The UV photolysis of the TA/Ar system was studied using both broad-band and narrow-band sources. The main photoproducts appeared to be carbodiimidylacetic acid and (1H-diaziren-3-yl)acetic acid. The progress of the reactions induced was followed by FTIR spectroscopy, whereas interpretation of the results was supported by quantum chemical calculations (DFT, TD-DFT).

Photochemical transformations of 5-methyltetrazole. Matrix isolation FTIR and DFT studies

Abstract In situ photolysis of 5-methyltetrazole (MT) isolated in low temperature argon matrices was induced by tunable UV laser radiation. The progress of the reactions was followed by FTIR spectroscopy that allowed for spectroscopic identification of three photoproducts resulting from the MT ring cleavage, namely C-methylnitrilimine CH3CNNH, N-methylcarbodiimide CH3NCNH, methylcyanamide CH3NHCN. The kinetic profiles obtained for these products show different behavior of the species in the course of irradiation. The N-methylcarbodiimide molecules were found to decompose further into two HCN or HNC molecules that interact in the matrix cages to form different hydrogen bonded dimers. Interpretation of the observed photoprocesses was supported by quantum chemical calculations (DFT, TD-DFT).

Photochemistry of the Ozone–Water Complex in Cryogenic Neon, Argon, and Krypton Matrixes

The photochemistry of ozone-water complexes and the wavelength dependence of the reactions were studied by matrix isolation FTIR spectrometry in neon, argon, and krypton matrixes. Hydrogen peroxide was formed upon the irradiation of UV light below 355 nm. Quantitative analyses of the reactant and product were performed to evaluate the matrix cage effect of the photoreaction. In argon and krypton matrixes, a bimolecular O((1)D) + H2O → H2O2 reaction was found to occur to form hydrogen peroxide, where the O((1)D) atom generated by the photolysis of ozone diffused in the cryogenic solids to encounter water. In a neon matrix, hydrogen peroxide was generated through intracage photoreaction of the ozone-water complex, indicating that a neon matrix medium is most appropriate to study the photochemistry of the ozone-water complex.

Conformational composition of neutral leucine. Matrix isolation infrared and ab initio study

Low-temperature matrix-isolation FTIR spectroscopy and ab initio calculations are employed to determine conformational composition of neutral leucine. The presence of three leucine conformers in the matrices is revealed. This is in agreement with the results of a detailed study of the potential energy surface of leucine which demonstrates that only five out of 105 possible conformers should have populations in the matrices larger than 2% and only three conformers, which are the ones detected in the experiment, should have populations larger than 10%. UV irradiation of the matrix samples are used to separate bands of the different conformers. We also show that the populations of the leucine conformers in the gas phase at 440K are significantly different from the ones in matrices. The population of the lowest energy conformer in the gas phase being approximately 23% in the gas phase increases to over 64% in matrices.

Matrix isolation FT-IR and theoretical DFT/B3LYP spectrum of 1-Naphthol

The FT-IR spectrum of 1-Naphthol isolated in an argon matrix is performed and compared to the infrared spectra calculated at the DFT (B3LYP)/6-31+G(d) level for cis-1-Naphthol and trans-1-Naphthol rotamers in order to clarify the existence of both rotamers in the standard temperature. Comparison of the computed and the experimental matrix spectra reveals the presence in 1-Naphthol argon matrices in the standard temperature of both cis and trans rotameric forms of 1-Naphthol, the last predominating. The relative stability of the trans-1-Naphthol rotamer has also been supported by a fit comparison between the difference of predicted total energy (ETC) of both rotamers of 0.00195a.u. corresponding to 5.12kJmol−1 and the variation of the standard free Gibbs energy of rotamerization (ΔGr°) of 5.06kJmol−1.Almost all 51 active vibrational modes of 1-Naphthol have been assigned. The stretching vibration of the OH group (νOH) appears to be the unique vibrational mode distinguishing the cis-1-NpOH rotamer from the trans-1-NpOH rotamer in FT-IR spectrum.

Conformational Landscape, Photochemistry, and Infrared Spectra of Sulfanilamide

A combined matrix isolation FTIR and theoretical DFT(B3LYP)/6-311++G(3df,3pd) study of sulfanilamide (SA) was performed. The full conformational search on the potential energy surface of the compound allowed the identification of four different minima, all of them bearing the sulfamide nitrogen atom placed in the perpendicular orientation relatively to the aromatic ring and differing from each other in the orientation of the hydrogen atoms connected to the two nitrogen atoms of the molecule. All conformers were predicted to be significantly populated in the gas phase (at 100 °C, their relative populations were estimated as being 1:0.9:0.3:0.2). However, in agreement with the theoretically calculated low-energy barriers for conformational isomerization, in the low-temperature matrices, only the most stable conformer could be observed, with the remaining forms being converted into this form during matrix deposition (conformational cooling). The unimolecular photochemistry of matrix-isolated SA (in both argon and xenon) was also investigated. Upon broadband UV irradiation (λ > 215 nm), two photofragmentation pathways were observed: the prevalent pathway (A), leading to extrusion of sulfur dioxide and simultaneous formation of benzene-1,4-diamine, which then converts to 2,5-cyclohexadiene-1,4-diimine, and the minor pathway (B), conducting an γ-cleavage plus [1,3] H-atom migration from the sulfamide group to the aromatic ring, which leads to formation of iminosulfane dioxide and aniline, the latter undergoing subsequent phototransformation into cyclohexa-2,5-dien-1-imine. Finally, the crystalline polymorph of SA resulting from warming (265 K) the amorphous solid obtained from fast cooling of the vapor of the compound onto the cold (13 K) substrate of the cryostat was identified spectroscopically, and found to be the γ-crystalline phase, the one exhibiting in average longer H-bonds and an infrared spectrum resembling more that of the low temperature SA glass. Full assignment of the infrared spectra of this crystalline variety as well as of those of the β-polymorph room temperature crystalline sample and low temperature amorphous state was undertaken with help of theoretical results obtained for the crystallographically relevant dimer of SA.

Conformational properties and photochemistry of new allyl tetrazoles: Matrix isolation FTIR and computational approach

Abstract The photochemistry and molecular structure of 1-allyltetrazole (1-ALT) and 2-allyltetrazole (2-ALT) were studied in argon matrices by infrared spectroscopy and B3LYP/6-311++G(2d,2p) calculations. Both allyltetrazoles were found to possess three stable conformers (1-ALT1, 1-ALT2, 1-ALT3 and 2-ALT1, 2-ALT2, 2-ALT3) differing in the orientation of the allyl group relative to the ring. Matrix isolation technique together with the annealing experiments allowed for detection of all 1-ALT and 2-ALT conformers. A conformational cooling phenomenon was observed for the 1-ALT3 → 1-ALT1 process in agreement with the predicted low energy barrier of 4.84 kJ mol −1 for this reaction. The broad-band UV irradiation of 1-ALT/Ar and 2-ALT/Ar matrices led to the same photoproducts. The main product N-allylcarbodiimide (P1) and two minor photoproducts allylcyanamide (P2) and C-allylnitrilimine (P3) are formed through the tetrazole ring cleavage and N 2 elimination. None of these molecules have been described before.