Matrix Isolation Spectroscopy Research Articles

Characterization of iso-CF2I2 in frequency and ultrafast time domains

The photolysis of diiododifluoromethane (CF(2)I(2)) in condensed phases was studied by a combination of matrix isolation and ultrafast time-resolved spectroscopy, in concert with ab initio calculations. Photolysis at wavelengths of 355 or 266 nm of CF(2)I(2):Ar samples (1:5000) held at approximately 8 K yielded iso-CF(2)I(2) (F(2)C-I-I), a metastable isomer of CF(2)I(2), characterized here for the first time. The infrared (IR) spectra of this isomer were recorded in matrix experiments, and the derived positions of the C-F stretching modes are in very good agreement with the predictions of high level ab initio calculations, which show that the iso-form is a minimum on the CF(2)I(2) ground state potential energy surface. The formation of this isomer following 350 nm excitation of CF(2)I(2) in room temperature CCl(4) solutions was monitored through its intense C-F stretching mode by means of ultrafast time-resolved IR absorption. Together, matrix isolation and ultrafast IR absorption experiments suggest that the formation of iso-CF(2)I(2) occurs via recombination of CF(2)I radical and I atom. Ultrafast IR experiments detect a delayed rise of iso-CF(2)I-I absorption, placing an upper limit of 400 fs for the C-I bond dissociation and primary geminate recombination processes. The product absorption spectrum recorded 1 ns after 350 nm excitation of CF(2)I(2) in solution is virtually identical to the visible absorption spectrum of iso-CF(2)I(2) trapped in matrix isolation experiments [with subtracted I(2)(X) absorption]. The formation of this isomer in solution at room temperature has direct dynamic implications for the ultrafast production of molecular iodine from electronically excited CF(2)I(2).

Visible photodissociation spectroscopy of PAH cations and derivatives in the PIRENEA experiment

The electronic spectra of gas-phase cationic polycyclic aromatic hydrocarbons (PAHs), trapped in the Fourier Transform Ion Cyclotron Resonance cell of the PIRENEA experiment, have been measured by multiphoton dissociation spectroscopy in the 430–480 nm spectral range using the radiation of a mid-band optical parametric oscillator laser. We present here the spectra recorded for different species of increasing size, namely the pyrene cation ( C 16 H 10 + ) , the 1-methylpyrene cation ( CH 3 C 16 H 9 + ) , the coronene cation ( C 24 H 12 + ) , and its dehydrogenated derivative C 24 H 10 + . The experimental results are interpreted with the help of time-dependent density functional theory calculations and analysed using spectral information on the same species obtained from matrix isolation spectroscopy data. A kinetic Monte Carlo code has also been used, in the case of pyrene and coronene cations, to estimate the absorption cross-sections of the measured electronic transitions. Gas-phase spectra of highly reactive species such as dehydrogenated PAH cations are reported for the first time.

ELECTRONIC SPECTROSCOPY OF MEDIUM-SIZED POLYCYCLIC AROMATIC HYDROCARBONS: IMPLICATIONS FOR THE CARRIERS OF THE 2175 Å UV BUMP

Mixtures of polycylic aromatic hydrocarbons (PAHs) have been produced by means of laser pyrolysis. The main fraction of the extracted PAHs were primarily medium-sized, up to a maximum size of 38 carbon atoms per molecule. The use of different extraction solvents and subsequent chromatographic fractionation provided mixtures of different size distributions. UV-VIS absorption spectra have been measured at low temperature by matrix isolation spectroscopy and at room temperature with PAHs as film-like deposits on transparent substrates. In accordance with semi-empirical calculations, our findings suggest that large PAHs with sizes around 50 to 60 carbon atoms per molecule could be responsible for the interstellar UV bump at 217.5 nm.

Attempted Isolation and Characterization of Diazirinone (N2CO)

Stimulated and intrigued by the report of the synthesis of diazirinone (1), a metastable adduct of N(2) and CO, we carried out further experimental and theoretical studies aimed at the detailed spectroscopic characterization of this species. Our attempts to generate and detect diazirinone (1) in either the condensed phase (using matrix isolation spectroscopy) or in the gas phase (using millimeter-wave rotational spectroscopy), however, have been unsuccessful. Trapping the volatile products produced from the reaction of 3-chloro-3-(p-nitrophenoxy)diazirine (5) with tetrabutylammonium fluoride (TBAF) under matrix-isolation conditions affords chlorofluorodiazirine (8) and carbon monoxide but fails to provide evidence for diazirinone (1). Moreover, sophisticated ab initio calculations of the structure and fundamental vibrational frequencies of diazirinone (1) produce an estimate for the fundamental band origin of the C=O stretch (2046 cm(-1)) that is ca. 100 cm(-1) lower in frequency than the experimental value previously attributed to this band. This discrepancy lies well outside any expected solvent shift or calculation error at this level of theory. In an effort to reconcile our findings with the earlier reports concerning diazirinone (1), we reconsidered the infrared spectral evidence upon which the original claim of diazirinone synthesis was based. New experiments demonstrate that these spectra may be explained and reproduced with a combination of solution-phase and gas-phase absorptions of CO, without recourse to invoke diazirinone (1).

Aqueous hydrogen bonding probed with polarization and matrix isolation spectroscopy

A major challenge in hydrogen-bond research is interpreting the vibrational spectrum of water, arguably the most fundamental hydrogen bonding system. This challenge remains despite over a half century of progress in vibrational spectroscopy, largely due to a combination of the huge oscillator strength and the enormous width of the hydrogen-bond region. Lack of assignment of the resonances in the hydrogen-bond region hinders investigation of interactions between water and solutes. This lack-of-interpretation issue is an even more significant problem for studies of the aqueous interface. Numerous solutes are known to have an effect, some very dramatic, on the shape of the surface spectrum. These effects, however, are but tantalizing teasers because lack of interpretation means that the changes cannot be used to diagnose the effect of solutes or impinging gas-phase molecules on the surface. In the reported work two techniques are used to probe the origin of vibrational resonances in the H-bonded region: the surface sensitive technique sum frequency generation (SFG) and room-temperature matrix isolation spectroscopy (RT-MIS). A polarization technique called polarization angle null (PAN) has been developed that extends SFG and enables identification of resonances. The result of applying PAN–SFG to single crystal, I h ice is identification of at least nine underlying resonances and assignment of two of these. One resonance is correlated with the crystal temperature and is a sensitive probe for interactions that disrupt long range order on the surface – it is a morphology reporter. The second is associated with weakly bonded, double-donor water molecules. This resonance is sensitive to interaction of hydrogen bond donors, i.e. acids, with the surface. Both modes are more correctly pictured as collective modes. These two assignments are the first definitive assignments in the hydrogen-bond region for the aqueous surface. The effect of salts on the vibrational spectrum of water is also probed with a recently developed room-temperature, matrix-isolation technique. The matrix environment demonstrates that salts containing large anions with small cations support water–water hydrogen bonds with a vibrational resonance that has similar characteristics as the SFG spectra of salt solutions.

Spectroscopic study of the reaction between Br2 and dimethyl sulfide (DMS), and comparison with a parallel study made on Cl2 + DMS: possible atmospheric implications

The reaction between molecular bromine and dimethyl sulfide (DMS) has been studied both as a co-condensation reaction in low temperature matrices by infrared (IR) matrix isolation spectroscopy and in the gas-phase at low pressures by UV photoelectron spectroscopy (PES). The co-condensation reaction leads to the formation of the molecular van der Waals adduct DMS-Br(2). This was identified by IR spectroscopy supported by results of electronic structure calculations. Calculation of the minimum energy structures in important regions of the reaction surface and computed IR spectra of these structures, which could be compared with the experimental spectra, allowed the structure of the adduct (C(s)) to be determined. The low pressure (ca. 10(-5) mbar) gas-phase reaction was studied by UV-PES, but did not yield any observable products, indicating that a third body is necessary for the adduct to be stabilised. These results are compared with parallel co-condensation and gas-phase reactions between DMS and Cl(2). For this reaction, a similar van der Waals adduct DMS-Cl(2) is observed by IR spectroscopy in the co-condensation reactions, but in the gas-phase, this adduct converts to a covalently bound structure Me(2)SCl(2), observed in PES studies, which ultimately decomposes to monochlorodimethylsulfide and HCl. For these DMS + X(2) reactions, computed relative energies of minima and transition states on the potential energy surfaces are presented which provide an interpretation for the products observed from the two reactions studied. The implications of the results obtained to atmospheric chemistry are discussed.

Matrix Isolation and Electronic Structure of Di- and Tridehydrobenzenes

Within the past four decades, matrix isolation spectroscopy has emerged as the method of choice for obtaining direct structural information on benzynes and related dehydroaromatics. In combination with quantum chemical computations, detailed insight into the structure and reactivity of di-, tri-, and tetradehydrobenzenes has been obtained. This Review focuses on rather recent developments in aryne chemistry with a special emphasis on the matrix isolation of tridehydrobenzenes and related systems.

Pulsed-jet discharge matrix isolation and computational study of CX 2Br + (X = H, F)

Pulsed-jet discharge matrix isolation spectroscopy and computational methods were used to characterize the CX 2Br + (X = H, F) ions. Our experiments combined matrix isolation techniques with a pulsed DC discharge nozzle, where a dilute CX 2Br 2:Ar sample was discharged and the products deposited onto a KBr window held at ∼8 K. This study represents the first spectroscopic observation of CH 2Br +, and the first report of the C–Br stretching frequency of CF 2Br +. Our results suggest that the primary mechanism for ion formation is ionization/fragmentation of the precursor by collision with metastable rare gas (Ar) atoms.

Photochemistry of Formaldoxime−Nitrous Acid Complexes in an Argon Matrix: Identification of Formaldoxime Nitrite

We have studied the structure and photochemistry of the formaldoxime−nitrous acid system (CH2NOH−HONO) by help of FTIR matrix isolation spectroscopy and ab initio methods. The MP2/6-311++G(2d,2p) calculations show stability of six isomeric CH2NOH···HONO complexes. The FTIR spectra evidence formation of two hydrogen bonded complexes in an argon matrix whose structures are determined by comparison of the experimental spectra with the calculated ones for the six stable complexes. In the matrix there is present the most stable cyclic complex with two O−H···N bonds; a strong bond is formed between the OH group of HONO and the N atom of CH2NOH and the weaker one between the OH group of CH2NOH and the N atom of HONO. In the other complex present in the matrix the OH group of formaldoxime is attached to the OH group of HONO forming an O−H···O bond. The irradiation of the CH2NOH···HONO complexes with the filtered output of the mercury lamp (λ > 345 nm) leads to the formation of formaldoxime nitrite, CH2NONO, and its two isomeric complexes with water. The main product is the CH2NONO···H2O complex in which water is hydrogen bonded to the N atom of the C═N group. The identity of the photoproducts is confirmed by both FTIR spectroscopy and MP2 or QCISD(full) calculations with the 6-311++G(2d,2p) basis set. The intermediate in this reaction is iminoxyl radical that is formed by abstraction of hydrogen atom from formaldoxime OH group by an OH radical originating from HONO photolysis.

Coupled-cluster calculations of C2H2Si and CNHSi structural isomers

Results of large-scale coupled-cluster calculations of selected C(2)H(2)Si and CNHSi structural isomers are reported. Equilibrium molecular structures of a total of 12 molecules in their singlet electronic states have been calculated systematically employing the coupled-cluster singles and doubles model augmented by a perturbative correction for triple excitations (CCSD(T)) in combination with Dunning's hierarchy of correlation consistent basis sets. In addition, anharmonic force fields were calculated to yield fundamental vibrational frequencies and rotation-vibration interaction constants alpha(i) (A,B,C). The latter were used to determine empirical equilibrium structures r(e) (emp) of two molecules - silacyclopropenylidene, c-C(2)H(2)Si, and silapropadienylidene, H(2)CCSi - for which sufficient isotopic data are available from literature. Very good agreement with theoretical equilibrium structures from CCSD(T) calculations employing core-valence basis sets of quadruple and quintuple-zeta quality - i.e., cc-pwCVQZ (337 basis functions), cc-pCV5Z, and cc-pwCV5Z (581 basis functions) is found - to within 0.001 A for bond lengths and 0.1 degrees for bond angles. Theoretical ground state rotational constants of HSiCN and HSiNC compare very favorably with experimental microwave data from literature, to within 0.15% (HSiCN) and 0.1% (HSiNC) for the B(0) and C(0) rotational constants. In the case of c-C(2)H(2)Si and H(2)CCSi this agreement is even better than 0.1%. For the latter two molecules effects of higher-level electron-correlation and relativity to the equilibrium geometry as well as the electronic contributions to the rotational constants are investigated. For eight molecules not yet studied at high spectral resolution in the gas-phase theoretical molecular parameters are provided to support future laboratory investigations. Theoretical vibrational fundamentals compare well with data of eight species studied previously with infrared matrix isolation spectroscopy.

A comprehensive study of (CH3)2CHOC(S)SC(O)OCH3using matrix isolation technique, X‐ray analysis, spectroscopic studies and theoretical calculations

AbstractPotassium isopropyl xanthate, (CH3)2CHOC(S)SK, reacts with methyl chloroformiate ClC(O)OCH3to yield (methoxycarbonyl) (2‐propoxythiocarbonyl) sulfide, (CH3)2CHOC(S)SC(O)OCH3. This novel xanthogen formate was characterized by1H and13C{1H} NMR spectroscopy, mass spectrometry and IR and Raman spectroscopy. The structure of a single crystal of (CH3)2CHOC(S)SC(O)OCH3was determined by X‐ray diffraction analysis at 173 K. The conformational properties have been studied by liquid IR and Raman spectroscopy, matrix isolation spectroscopy together with photochemical studies and quantum chemical calculations (HF and B3LYP methods with the 6‐31+G* basis set). The analysis of the IR spectrum of liquid (CH3)2CHOC(S)SC(O)OCH3suggests the presence of two conformers in equilibrium at room temperature. However, in the photochemical matrix study, an equilibrium of three conformers was detected. These forms were further characterized by theoretical calculations. Different photolysis products, such as CH3OC(O)SCH(CH3)2, OCS, CO, CO2and CS2, were identified by matrix spectroscopy. The IR absorptions of CH3OC(O)SCH(CH3)2, for which literature data are scarce, were analysed in the light of the results of appropriate theoretical calculations. Copyright © 2009 John Wiley & Sons, Ltd.

IR photodissociation spectroscopy of O 4+, O 6+ and O 8+ cluster ions

O 4 + and larger (O 2) n + cluster ions are produced in a pulsed discharge source and studied with time-of-flight mass spectrometry and infrared laser photodissociation spectroscopy. The infrared laser photon energies used allow bracketing of the cluster dissociation energies. Sharp resonant structure is detected for each of these ions in the region of the O–O stretching vibrations and also at higher frequencies corresponding to combination bands. Although previous matrix isolation spectroscopy on O 4 + found evidence for both trans-bent and rectangular isomers of this ion, the gas phase IR spectrum only contains bands assigned to the rectangular isomer. O 6 + has a distinctive IR spectrum unlike that for O 4 +, indicating that it is not simply a solvated O 4 + species, while O 8 + has the signature of a solvated O 6 + ion.

Matrix Isolation and Ab Initio Study of the Noncovalent Complexes between Formamide and Acetylene

Matrix isolation spectroscopy in combination with ab initio calculations is a powerful technique for the identification of weakly bound intermolecular complexes. Here, weak complexes between formamide and acetylene are studied, and three 1:1 complexes with binding energies of -2.96, -2.46, and -1.79 kcal/mol have been found at the MP2 level of theory (MP2/cc-pVTZ + ZPE + BSSE). The two most stable dimers A and B are identified in argon and nitrogen matrices by comparison between the experimental and calculated infrared frequencies. Both complexes are stabilized by the formamide C=O...HC acetylene and H...pi interactions. Large shifts have been observed experimentally for the C-H stretching vibrations of the acetylene molecule, in very good agreement with the calculated values. Eight 1:2 FMA-acetylene trimers (T-A to T-H) with binding energies between -5.44 and -2.62 kcal/mol (MP2/aug-cc-pVDZ + ZPE + BSSE) were calculated. The two most stable trimers T-A and T-B are very close in energy and have similar infrared spectra. Several weak bands that are in agreement with the calculated frequencies of the trimers T-A and T-B are observed under matrix isolation conditions. However, the differences are too small for a definitive assignment.

Infrared signatures of the NCCO radical

The first definitive infrared signatures of the elusive NCCO radical have been measured using a microwave discharge technique combined with low-temperature matrix-isolation spectroscopy, resulting in a consistent set of vibrational assignments for six isotopologues. The infrared spectra of these NCCO isotopologues were concomitantly established by rigorous variational nuclear-motion computations based on a high-level coupled-cluster quartic vibrational force field [ROCCSD(T)/cc-pCVQZ] and cubic dipole field [ROCCSD/cc-pCVTZ]. Our experimental and theoretical results for NCCO overturn the vibrational assignments in a NIST-JANAF compilation and those from a recent two-dimensional cross-spectral correlation analysis. For the parent isotopologue at 11 K in a nitrogen matrix, we find the signature bands nu(2)(CO str.) = 1889.2 cm(-1) and nu(3)(CC str.) = 782.0 cm(-1). Our variational vibrational computations reveal strong mixing of the nu(3) stretching fundamental and the nu(4) + nu(5) bending combination level for all isotopologues. These Fermi resonances manifest a clear breakdown of the simple normal-mode picture of molecular vibrations at low energies.

Spectroscopy of Jet-Cooled Bi3

A resonant two-photon ionization spectroscopic study of jet-cooled Bi3 has identified two band systems in the molecule in the 9600-10 600 and 15 250-16 050 cm(-1) range. The latter of these has been previously observed in matrix isolation spectroscopy and tentatively attributed to Bi4; the mass-resolved work presented here reassigns it to Bi3. A review of all previously observed electronic states is presented, and it is argued that the new band system lying in the range 9600-10 600 cm(-1) corresponds to the spin-forbidden A' 4A1" <-- X1 2E" (E1/2 component) band system.

Conformational and structural analysis of 2-allyl-1,2-benzisothiazol-3(2 H)-one 1,1-dioxide as probed by matrix-isolation spectroscopy and quantum chemical calculations

2-Allyl-1,2-benzisothiazol-3(2 H)-one 1,1-dioxide (ABIOD) has been studied by matrix-isolation infrared spectroscopy and quantum chemical calculations. A conformational search on the B3LYP/6 -311++G(3df,3pd) potential energy surface of the molecule demonstrated the existence of three conformers, Sk, Sk′ and C, with similar energies, differing in the orientation of the allyl group. The calculations predicted the Sk form as the most stable in the gaseous phase, whereas the Sk′ and C conformers have calculated relative energies of ca. 0.6 and 0.8–3.0 kJ mol −1, respectively (depending on the level of theory). In agreement with the relatively large (>6 kJ mol −1) calculated barriers for conformational interconversion, the three conformers could be efficiently trapped in an argon matrix at 10 K, the experimental infrared spectrum of the as-deposited matrix fitting well the simulated spectrum built from the calculated spectra for individual conformers scaled by their predicted populations at the temperature of the vapour of the compound prior to matrix deposition. Upon annealing the matrix at 24 K, however, both Sk and Sk′ conformers were found to convert to the more polar C conformer, indicating that this latter form becomes the most stable ABIOD conformer in the argon matrix.

Photo‐Induced Hydrogen Exchange Reaction between Methanol and Glyoxal: Formation of Hydroxyketene

We study the structure and photochemistry of the glyoxal-methanol system (G-MeOH) by means of FTIR matrix isolation spectroscopy and ab initio calculations. The FTIR spectra show that the non-hydrogen-bonded complex, G-MeOH-1, is present in an inert environment of solid argon. MP2/aug-cc-pVDZ calculations indicate that G-MeOH-1 is the most stable complex among the five optimized structures. The interaction energy partitioned according to the symmetry-adapted perturbation theory (SAPT) scheme demonstrates that the dispersion energy gives a larger contribution to the stabilization of a non-hydrogen-bonded G-MeOH-1 complex than compared to the hydrogen-bonded ones. The irradiation of G-MeOH-1 with the filtered output of a mercury lamp (lambda>370 nm) leads to its photo-conversion into the hydroxyketene-methanol complex HK-MeOH-1. The identity of HK-MeOH-1 is confirmed by both FTIR spectroscopy and MP2/aug-cc-pVDZ calculations. An experiment with deuterated methanol (CH(3)OD) evidences that hydroxyketene is formed in a photo-induced hydrogen exchange reaction between glyoxal and methanol. The pathway for the photo-conversion of G-MeOH-1 to HK-MeOH-1 is studied by a coupled-cluster method [CR-CC(2,3)]. The calculations confirm our experimental findings that the reaction proceeds via hydrogen atom exchange between the OH group of methanol and CH group of glyoxal.

Complexation of formaldoxime and acetaldoxime with nitrogen

The complexes formed between formaldoxime (FNOH) or Z- and E-acetaldoxime ( Z-AcNOH, E-AcNOH) and nitrogen have been studied by FTIR matrix isolation spectroscopy and by ab initio MP2/6-311++G(2d, 2p) calculations. The calculations showed the stability of seven structures for the 1:1 FNOH···N 2, Z-AcNOH···N 2 and E-AcNOH···N 2 complexes; the most stable of the seven structures is that with the N 2 attached to the OH group of the oxime. The stability of the corresponding complexes is in the following energetic order: E (FNOH···N 2) < E ( E-AcNOH···N 2) < E ( Z-AcNOH···N 2). The FTIR spectra evidence that in the argon matrices the most stable 1:1 structures are present. The spectra indicate also the formation of the other structures for these systems however their concentration is much lower than the concentrations of the most stable complexes. The quantitative spectra analysis demonstrated that Z-AcOH···N 2 complexes are more readily formed than the E-AcOH···N 2 ones indicating the higher acidity of the first isomer with respect to the second one. In the matrices with larger concentration of nitrogen the 1:2 formaldoxime-nitrogen complex was also identified and its structure is discussed on the basis of theoretical spectra calculated for the eleven optimized FNOH···(N 2) structures.

Apparatus for High-Resolution Solid Hydrogen Matrix Isolation Spectroscopy and Its Application

Apparatus integrating a Fourier transform-infrared (FT-IR) spectrometer and a mid-infrared difference frequency generation (DFG) laser spectrometer was built for the study of the matrix isolation spectrum in solid molecular hydrogen. A 3-cm-long molecular hydrogen crystal was grown in a liquid-helium Dewar, and its infrared absorption spectrum in the 1-5 μm region was recorded to test the system. The W 0(0) (ν=0←0, J=6←0) line around 2410 cm −1 of solid hydrogen was investigated with the DFG laser spectroscopy. High-resolution matrix isolation spectrum of CO 2 co-deposited with hydrogen on a BaF 2 cold plate at liquid-helium temperature was studied.

Direct Observation of Microscopic Solvation at the Surface of Clusters by Ultrafast Photoelectron Imaging

We report on microscopic observation of solvation by argon atoms of excited states of an ethylenic-like molecule, TDMAE (tetrakis dimethylaminoethylene). Two experimental methods were used: gas phase dynamics for the observation of the evolution through excited states, matrix isolation spectroscopy for characterization of the initial states. Excited state dynamics was recorded after the molecule had been deposited on the surface of a large argon cluster (n approximately 100) by pick-up. The deposited cluster was characterized by mass spectrometry and by its shifted photoelectron spectrum. The time evolution of the system was visualized by femtosecond pump/probe velocity map imaging of photoelectrons. The time evolution of deposited TDMAE excited at 266 nm can be modeled via a modified three state model, as in the free molecule. The initially excited state is of valence character, and a Rydberg state mediates the passage to a zwitterionic configuration. The specific solvation of Rydberg states by the surface of the cluster was directly observed and is discussed. It represents the striking outcome of the present work. It is inferred that differently from the gas phase, solvated Rydberg states resulting from state mixing within a R(n/lambda) complex in the presence of the argon surface are reached. Solvation of these Rydberg states should be effective through interaction of the ion core of the excited molecules with the cluster.