Infrared spectra of the C2H2-(OCS)2 van der Waals complex: observation of a structure with C2 symmetry

Infrared spectra of the C(2)H(2)-(OCS)(2) trimer are studied by means of direct infrared absorption spectroscopy. The van der Waals complexes are generated in a supersonic slit-jet apparatus and probed using a rapid-scan tunable diode laser in the region of the ν(1) fundamental vibration of the OCS monomer. Two infrared bands are analyzed for the lowest energy isomer of the trimer, which has C(2) symmetry and is experimentally observed here for the first time. A relatively strong band centered at 2068.93 cm(-1) is assigned as the out-of-phase vibrations of the pair of equivalent OCS monomers. This band is blue-shifted relative to the free OCS monomer but with a reduced shift as compared with the analogous vibration of the nonpolar OCS dimer. A weaker red-shifted band observed at 2049.64 cm(-1) establishes the nonplanarity of the OCS dimer subunit within the trimer. Spectra for three isotopologues in addition to the normal form are used to help define an experimental structure, which agrees well with past and present semiempirical calculations.     

Infrared spectrum of the CS2 trimer: observation of a structure with D3 symmetry

Infrared spectra of a carbon disulfide trimer formed in a pulsed supersonic slit-jet expansion are obtained via direct absorption of a tuneable diode laser in the region of the CS(2)ν(3) fundamental (～1535 cm(-1)). This is the first high-resolution spectroscopic observation of (CS(2))(3). Two bands sharing the same lower state are assigned to ((12)C(32)S(2))(3). These correspond to the two infrared active trimer vibrations (a parallel and a perpendicular band) of the constituent CS(2) monomer asymmetric stretches. The weaker perpendicular band is centered at 1524.613 cm(-1), shifted by -10.74 cm(-1) with respect to the free CS(2) monomer. The parallel band is centered at 1545.669 cm(-1), a vibrational shift of +10.31 cm(-1). Transitions with K≠ 3n and those with K = 0, J = odd in the ground state are absent, establishing that this trimer has D(3) symmetry. The two parameters required to define this structure are determined to be 3.811 ? for the C-C bond distance and 61.8° for the angle between a monomer axis and the plane containing the C atoms. In addition, a parallel band arising from trimers with a single (34)S substitution is observed around 1544.46 cm(-1). Together with the recently observed cross-shaped CS(2) dimer, these results indicate a tendency for CS(2) to form highly symmetric clusters.     

The vibration-rotation emission spectrum of hot BeF2

The high-resolution infrared emission spectrum of BeF2 vapor at 1000 degrees C was rotationally analyzed with the assistance of large-scale ab initio calculations using the coupled-cluster method including single and double excitations and perturbative inclusion of triple excitations, in conjunction with correlation-consistent basis sets up to quintuple-zeta quality. The nu3 fundamental band, the nu1+nu2, nu1+nu3, and 2nu2+nu3 combination bands, and 18 hot bands were assigned. The symmetric stretching (nu1), bending (nu2), and antisymmetric stretching (nu3) mode frequencies were determined to be 769.0943(2), 342.6145(3), and 1555.0480(1) cm-1, respectively, from the band origins of the nu3, nu1+nu3, and nu1+nu2 bands. The observed vibrational term values and B rotational constants were fitted simultaneously to an effective Hamiltonian model with Fermi resonance taken into account, and deperturbed equilibrium vibrational and rotational constants were obtained for BeF2. The equilibrium rotational constant (Be) was determined to be 0.235 354(41) cm-1, and the associated equilibrium bond distance (re) is 1.3730(1) A. The results of our ab initio calculations are in remarkably good agreement with those of our experiment, and the calculated value was 1.374 A for the equilibrium bond distance (re). As in the isoelectronic CO2 molecule, the Fermi resonance in BeF2 is very strong, and the interaction constant k122 was found to be 90.20(4) cm-1.     

Infrared and infrared emission spectroscopy of the zinc carbonate mineral smithsonite

Infrared emission and infrared spectroscopy has been used to study a series of selected natural smithsonites from different origins. An intense broad infrared band at 1440cm(-1) is assigned to the nu(3) CO(3)(2-) antisymmetric stretching vibration. An additional band is resolved at 1335cm(-1). An intense sharp Raman band at 1092cm(-1) is assigned to the CO(3)(2-) symmetric stretching vibration. Infrared emission spectra show a broad antisymmetric band at 1442cm(-1) shifting to lower wavenumbers with thermal treatment. A band observed at 870cm(-1) with a band of lesser intensity at 842cm(-1) shifts to higher wavenumbers upon thermal treatment and is observed at 865cm(-1) at 400 degrees C and is assigned to the CO(3)(2-)nu(2) mode. No nu(2) bending modes are observed in the Raman spectra for smithsonite. The band at 746cm(-1) shifts to 743cm(-1) at 400 degrees C and is attributed to the CO(3)(2-)nu(4) in phase bending modes. Two infrared bands at 744 and around 729cm(-1) are assigned to the nu(4) in phase bending mode. Multiple bands may be attributed to the structural distortion ZnO(6) octahedron. This structural distortion is brought about by the substitution of Zn by some other cation. A number of bands at 2499, 2597, 2858, 2954 and 2991cm(-1) in both the IE and infrared spectra are attributed to combination bands.     

Infrared spectra of CO2-H2 complexes

Infrared spectra of weakly bound CO(2)-H(2) complexes have been studied in the region of the CO(2) v(3) asymmetric stretch, using a tunable diode laser probe and a pulsed supersonic jet expansion. For CO(2)-paraH(2), results were obtained for three isotopic species, (12)C(16)O(2), (13)C(16)O(2), and (12)C(18)O(2). These spectra were analyzed using an asymmetric rotor Hamiltonian, with results that resembled those obtained previously for OCS- and N(2)O-paraH(2), except that half the rotational levels were missing due to the symmetry of CO(2) and the spin statistics of the (16)O or (18)O nuclei. However, for CO(2)-orthoH(2), more complicated spectra were observed which could not be assigned, in contrast with OCS- and N(2)O-H(2) where the paraH(2) and orthoH(2) spectra were similar, though distinct. The CO(2)-paraH(2) complex has a T-shaped structure with and intermolecular distance of about 3.5 Angstroms, and the CO(2) v(3) vibration exhibits a small redshift (-0.20 cm(-1)) in the complex.     

Correlation of structure and vibrational spectra of the zwitterion L-alanine in the presence of water: an experimental and density functional analysis

Infrared vibrational spectra were collected along with the vibrational circular dichroism (VCD) spectra for the zwitterions alpha-D-alanine, alpha-L-alanine, alpha-D-mannose and alpha-L-mannose as potassium bromide (KBr) pressed samples. VCD for D- and L-alanine dissolved in water was also measured and compared against the spectra resulting from KBr pressed samples. The experimental data were compared against the ab initio B3LYP/6-31G* optimized geometry. The zwitterion structure of alpha-L-alanine was stabilized by the addition of water molecules. Computationally, beta-L-mannose was studied and resulting expected VCD bands assigned. We present the molecular structures resulting VCD spectra and infrared vibrational spectra from experimentation as compared with the computed results.     

SiH2Cl2: ab initio anharmonic force field, dipole moments, and infrared vibrational transitions

The vibrational spectra of SiH2Cl2 have been recorded in the 1000-13,000 cm(-1) region, utilizing the Fourier-transform spectroscopy and Fourier-transform intracavity laser absorption spectroscopy. Totally 61 band centers and intensities are derived from the infrared spectra. An ab initio quartic force field is obtained by applying the second-order Moller-Plesset perturbation theory and correlation-consistent polarized valence triplet-zeta basis sets [J. Chem. Phys. 90, 1007 (1989); 98, 1358 (1993)]. Most observed bands are assigned by the vibration analysis based on the second-order perturbation theory. Reduced-dimensional ab initio dipole moment functions (two dimensional and three dimensional) have also been calculated to investigate the absolute band intensities of the SiH2 chromophore. The calculated values agree reasonably with the observed ones.     

High-resolution infrared spectroscopy and ab initio studies of the cyclopropane-carbon dioxide interaction

A jet-cooled high-resolution infrared spectrum of the cyclopropane-carbon dioxide complex was detected for the first time, using a rapid scan infrared spectrometer with an astigmatic multipass sample cell. The spectrum was recorded in the vicinity of the CO2 asymmetric stretching band (nu3) and exhibits a b-dipole selection rule. Altogether, over 200 lines were observed, assigned, and fitted to Watson's S-reduction Hamiltonian. Rotational and quartic distortion constants were obtained. The band origin was located at 2347.6263(2) cm(-1), redshifted by 1.5230(2) cm(-1) from the corresponding frequency of the CO2 monomer. The experimentally determined structure shows that CO2 lies next to a C-C bond edge and is perpendicular to the C3 ring, indicating that the interaction is characterized by the bonding between the carbon atom of CO2 and the pseudo-pi system of cyclopropane. The intermolecular distance between the carbon atom of CO2 and the center of mass of cyclopropane was determined to be 3.667(2) A. Complete ab initio geometry optimizations and harmonic frequency calculations were carried out at the level of second-order Moller-Plesset perturbation theory with four different basis sets: cc-pVDZ, 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ. The lowest-energy structure identified with the three larger basis sets is in accord with the experimental finding. In addition, a transition state was identified and the tunneling barrier height was computed.     

Four tautomers of isolated guanine from infrared laser spectroscopy in helium nanodroplets

Infrared laser spectroscopy is used to study the four lowest energy tautomers of guanine, isolated in helium nanodroplets. The large number of vibrational bands observed in the infrared spectrum are assigned by comparing the corresponding experimental vibrational transition moment angles with those obtained from ab initio theory. The result is the conclusive assignment of the spectrum to the N9H-Keto, N7H-Keto, N9Ha-Enol(trans), and N9Hb-Enol(cis) tautomers. The dipole moments of these tautomers are also experimentally determined and compared with ab initio theory.     

The infrared spectrum of Au-.CO2

The Au-.CO2 ion-molecule complex has been studied by gas phase infrared photodissociation spectroscopy. Several sharp transitions can be identified as combination bands involving the asymmetric stretch vibrational mode of the CO2 ligand. Their frequencies are redshifted by several hundred cm(-1) from the frequencies of free CO2. We discuss our findings in the framework of ab initio and density-functional theory calculations, using anharmonic corrections to predict vibrational transition energies. The infrared spectrum is consistent with the formation of an aurylcarboxylate anion with a strongly bent CO2 subunit.     

Infrared absorption spectra of the CO(2)/H(2)O complex in a cryogenic nitrogen matrix--detection of a new bending frequency

Infrared absorption spectra have been measured for the mixture of CO(2) and H(2)O in a cryogenic nitrogen matrix. The 1:1 CO(2)/H(2)O complex has been observed. Each structure of this complex should have two bending frequencies corresponding to the CO(2) fundamental bending mode (ν(2)). In this work, three bending frequencies corresponding to the CO(2) fundamental bending mode (ν(2)) have been detected; one of them at 660.3 cm(-1) is reported here for the first time. This finding helps confirm the existence of two structures for this complex. A new feature attributed to a CO(2) and H(2)O complex is observed at 3604.4 cm(-1) and is tentatively assigned to the CO(2)/H(2)O complex band corresponding to the CO(2) combination mode (ν(3) + 2ν(2)). In addition, a band that belongs to a CO(2) and H(2)O complex is detected at 3623.8 cm(-1) for the first time and is tentatively assigned to the (CO(2))(2)/H(2)O complex band corresponding to the symmetric stretching mode (ν(1)) of H(2)O.     

Self-assembly organometallic squares with terpyridyl metal complexes as bridging ligands

A series of novel heterometallic square complexes with the general molecular formulas [fac-Br(CO)(3)Re[mu-(pyterpy)(2)M]](4)(PF(6))(8) and [(dppf)Pd[mu-(pyterpy)(2)Ru]](4)(PF(6))(8)(OTf(8) (4), where M = Fe (1), Ru (2), or Os (3), pyterpy is 4'-(4' "-pyridyl)-2,2':6',2' '-terpyridine, dppf = 1,1'-bis(diphenylphosphino)ferrocene and OTf is trifluoromethanesulfonate, were prepared by self-assembly between BrRe(CO)(5) or (dppf)Pd(H(2)O)(2)(OTf)(2) and (pyterpy)(2)M(PF(6))(2). The obtained NMR spectra, IR spectra, electrospray ionization mass spectra, and elemental analyses are all consistent with the proposed square structures incorporating terpyridyl metal complexes as bridging ligands. Multiple redox processes were observed in all square complexes. All four complexes display strong visible absorptions in the region 400-600 nm, which are assigned as metal (Fe, Ru, or Os)-to-ligand (pyterpy) charge transfer (MLCT) bands. Square 3 exhibits an additional weak band at 676 nm, which is assigned to an Os-based (3)MLCT band. For each complex, the bands centered between 279 and 377 nm are assigned as pyterpy-based pi-pi bands and the Re-based MLCT band. Square 3 is luminescent in room-temperature solution, while squares 1, 2, and 4 do not have any detectable luminescence under identical experimental conditions.     

The Dinitramide Anion, N(NO(2))(2)(-)

The infrared and Raman spectra of the NH(4)(+), K(+), and Cs(+) salts of N(NO(2))(2)(-) in the solid state and in solution have been measured and are assigned with the help of ab initio calculations at the HF/6-31G and MP2/6-31+G levels of theory. In agreement with the variations observed in the crystal structures, the vibrational spectra of the N(NO(2))(2)(-) anion are also strongly influenced by the counterions and the physical state. Whereas the ab initio calculations for the free N(NO(2))(2)(-) ion indicate a minimum energy structure of C(2) symmetry, Raman polarization measurements on solutions of the N(NO(2))(2)(-) anion suggest point group C(1) (i.e., no symmetry). This is attributed to the very small (<3 kcal/mol) N-NO(2) rotational barrier in N(NO(2))(2)(-) which allows for easy deformation.     

Infrared spectra of the Li+-(H2)n (n=1-3) cation complexes

The Li+-(H2)n n=1-3 complexes are investigated through infrared spectra recorded in the H-H stretch region (3980-4120 cm-1) and through ab initio calculations at the MP2/aug-cc-pVQZ level. The rotationally resolved H-H stretch band of Li+-H2 is centered at 4053.4 cm-1 [a -108 cm-1 shift from the Q1(0) transition of H2]. The spectrum exhibits rotational substructure consistent with the complex possessing a T-shaped equilibrium geometry, with the Li+ ion attached to a slightly perturbed H2 molecule. Around 100 rovibrational transitions belonging to parallel Ka=0-0, 1-1, 2-2, and 3-3 subbands are observed. The Ka=0-0 and 1-1 transitions are fitted by a Watson A-reduced Hamiltonian yielding effective molecular parameters. The vibrationally averaged intermolecular separation in the ground vibrational state is estimated as 2.056 A increasing by 0.004 A when the H2 subunit is vibrationally excited. The spectroscopic data are compared to results from rovibrational calculations using recent three dimensional Li+-H2 potential energy surfaces [Martinazzo et al., J. Chem. Phys. 119, 11241 (2003); Kraemer and Spirko, Chem. Phys. 330, 190 (2006)]. The H-H stretch band of Li+-(H2)2, which is centered at 4055.5 cm-1 also exhibits resolved rovibrational structure. The spectroscopic data along with ab initio calculations support a H2-Li+-H2 geometry, in which the two H2 molecules are disposed on opposite sides of the central Li+ ion. The two equivalent Li+...H2 bonds have approximately the same length as the intermolecular bond in Li+-H2. The Li+-(H2)3 cluster is predicted to possess a trigonal structure in which a central Li+ ion is surrounded by three equivalent H2 molecules. Its infrared spectrum features a broad unresolved band centered at 4060 cm-1.     

Spectroscopic observation and structure of CS2 dimer

Infrared spectra of the CS(2) dimer are observed in the region of the CS(2) ν(3) fundamental band (～1535 cm(-1)) using a tunable diode laser spectrometer. The weakly bound complex is formed in a pulsed supersonic slit-jet expansion of a dilute gas mixture of carbon disulfide in helium. Contrary to the planar slipped-parallel geometry previously observed for (CO(2))(2), (N(2)O)(2), and (OCS)(2), the CS(2) dimer exhibits a cross-shaped structure with D(2d) symmetry. Two bands were observed and analyzed: the fundamental (C-S asymmetric stretch) and a combination involving this mode plus an intermolecular vibration. In both cases, the rotational structure corresponds to a perpendicular (ΔK = ±1) band of a symmetric rotor molecule. The intermolecular center of mass separation (C-C distance) is determined to be 3.539(7) A?. Thanks to symmetry, this is the only parameter required to characterize the structure, if the monomer geometry is assumed to remain unchanged in the dimer. From the band centers of the fundamental and combination band an intermolecular frequency of 10.96 cm(-1) is obtained, which we assign as the torsional bending mode. This constitutes the first high resolution spectroscopic investigation of CS(2) dimer.     

Spectroscopic and structural elucidation of L-tyrosine-containing dipeptides valyl-tyrosine and tyrosyl-alanine: solid-state IR-LD spectroscopy, quantum chemical calculations and vibrational analysis

L-Tyrosine-containing dipeptides valyl-tyrosine (H-Val-Tyr-OH) and tyrosyl-alanine (H-Tyr-Ala-OH) are characterized structurally by means of quantum chemical ab initio calculations and solid-state linear-dichroic infrared (IR-LD) spectroscopy. The IR-characteristic bands are assigned by application of reducing-difference procedure for polarized IR-spectra interpretation. Infrared data obtained are supported as well by the made vibrational analysis. The structures of both peptides are predicted on the basis of conformational analysis and structural information, obtained by the shown IR-spectroscopic tool.     

Infrared laser spectroscopy of uracil and thymine in helium nanodroplets: vibrational transition moment angle study

Vibrational spectra are reported in the N-H stretching region for uracil and thymine monomers in helium nanodroplets. Each monomer shows only a single isomer, the global minimum, in agreement with previous experimental and theoretical studies. The assignment of the infrared vibrational bands in the spectra is aided by the measurement of the corresponding vibrational transition moment angles (VTMAs) and ab initio frequency calculations. The ambiguity in the VTMA assignment of the N3H band for the uracil monomer is explained by the presence of dimer bands, which are overlapped with the monomer band.     

High resolution infrared spectroscopy of carbon dioxide clusters up to (CO2)13

Thirteen specific infrared bands in the 2350 cm(-1) region are assigned to carbon dioxide clusters, (CO(2))(N), with N = 6, 7, 9, 10, 11, 12 and 13. The spectra are observed in direct absorption using a tuneable infrared laser to probe a pulsed supersonic jet expansion of a dilute mixture of CO(2) in He carrier gas. Assignments are aided by cluster structure calculations made using two reliable CO(2) intermolecular potential functions. For (CO(2))(6), two highly symmetric isomers are observed, one with S(6) symmetry (probably the more stable form), and the other with S(4) symmetry. (CO(2))(13) is also symmetric (S(6)), but the remaining clusters are asymmetric tops with no symmetry elements. The observed rotational constants tend to be slightly (≈2%) smaller than those from the predicted structures. The bands have increasing vibrational blueshifts with increasing cluster size, similar to those predicted by the resonant dipole-dipole interaction model but significantly larger in magnitude.     

UV photolysis products of propiolic acid in noble-gas solids

Photolysis (193 nm) of propiolic acid (HCCCOOH) was studied with Fourier transform infrared spectroscopy in noble-gas (Ar, Kr, and Xe) solid matrixes. The photolysis products were assigned using ab initio quantum chemistry calculations. The novel higher-energy conformer of propiolic acid was efficiently formed upon UV irradiation, and it decayed back to the ground-state conformer on a time scale of approximately 10 min by tunneling of the hydrogen atom through the torsional energy barrier. In addition, the photolysis produced a number of matrix-isolated 1:1 molecular complexes such as HCCH...CO2, HCCOH...CO, and H2O...C3O. The HCCH...CO2 complex dominated among the photolysis products, and the computations suggested a parallel geometry of this complex characterized by an interaction energy of -9.6 kJ/mol. The HCCOH...CO complex also formed efficiently, but its concentration was strongly limited by its light-induced decomposition. In this complex, the most probable geometry was found to feature the interaction of carbon monoxide with the OH group via the carbon atom, and the computational interaction energy was determined to be -18.3 kJ/mol. The formation of the strong H2O...C3O complex (interaction energy -21 kJ/mol) was less efficient, which might be due to the inefficiency of the involved radical reaction.     

Assignment of rovibrational transitions of propyne in the region of 2934-2952 cm(-1) measured by two-color IR-vacuum ultraviolet laser photoion-photoelectron methods

The infrared (IR) spectrum of propyne in the region of 2934-2952 cm(-1) has been recorded by the IR-vacuum ultraviolet (VUV)-photoion method. The spectrum is shown to consist of two near-resonant, but noncoupled vibrational bands: the nu2 symmetric methyl C-H stretching vibrational band and a combination vibrational band nucs. The previously unobserved Q line of the nucs band is observed. The rotational transition lines of the nu2=1 band produces IR-VUV-pulsed field ionization-photoelectron (IR-VUV-PFI-PE) signal at the C3H4+ (nu2+=1) photoionization threshold. The rotational transition lines associated with the nucs band do not produce IR-VUV-PFI-PE signal. Rotational transition lines of both vibrational bands are assigned and simulated; and ab initio calculations further confirm the assignment.