Infrared spectra of seeded hydrogen clusters: (paraH2)N - OCS, (orthoH2)N - OCS, and (HD)N - OCS, N = 2 - 7

Infrared spectra of hydrogen-carbonyl sulfide clusters containing paraH2, orthoH2, or HD have been studied in the 2060 cm(-1) region of the C-O stretching vibration. The clusters were formed in pulsed supersonic jet expansions and probed using a tunable infrared diode laser spectrometer. Simple symmetric rotor type spectra were observed and assigned for clusters containing up to N = 7 hydrogen molecules. There was no resolved K structure, and Q-branch features were present for orthoH2 and HD but absent for paraH2. These characteristics can be rationalized in terms of near symmetric rotor structures, very low effective rotational temperatures (0.15 to 0.6 K), and nuclear spin statistics. The observed vibrational shifts were compared with those from recent observations on the same clusters embedded in helium nanodroplets. The observed rotational constants for the paraH2 clusters are in good agreement with a recent quantum Monte Carlo simulation. Some mixed clusters were also observed, such as HD-HD-He-OCS and paraH2 - orthoH2 - OCS.     

Vibrational shifts of OCS in mixed clusters of parahydrogen and helium

We present a detailed theoretical study of the solvation structure and solvent induced vibrational shifts for an OCS molecule embedded in pure parahydrogen clusters and in mixed parahydrogen/helium clusters. The use of two recent OCS-(parahydrogen) and OCS-helium ab initio potential energy surfaces having explicit dependence on the asymmetric stretch of the OCS molecule allows calculation of the frequency shift of the OCS nu(3) vibration as a function of the cluster size and composition. We present results for clusters containing up to a full first solvation shell of parahydrogen (N=17 molecules), and up to M=128-N helium atoms. Due to the greater interaction strength of parahydrogen than helium with OCS, in the mixed clusters the parahydrogen molecules always displace He atoms in the first solvation shell around OCS and form multiple axial rings as in the pure parahydrogen clusters. In the pure clusters, the chemical potential of parahydrogen shows several magic numbers (N=8,11,14) that reflect an enhanced stability of axial rings containing one less molecule than required for complete filling at N=17. Only the N=14 magic number survives in the mixed clusters, as a result of different filling orders of the rings and greater delocalization of both components. The OCS vibration shows a redshift in both pure and mixed clusters, with N-dependent values that are in good agreement with the available experimental data. The dependence of the frequency shift on the cluster size and its composition is analyzed in terms of the parahydrogen and helium density distributions around the OCS molecule as a function of N and M. The frequency shift is found to be strongly dependent on the detailed distribution of the parahydrogen molecules in the pure parahydrogen clusters, and to be larger but show a smoother dependence on N in the presence of additional helium, consistent with the more delocalized nature of the mixed clusters.     

Infrared spectra and ab initio calculations for the F- -(CH4)n (n = 1-8) anion clusters

Infrared spectra of mass-selected F- -(CH4)n (n = 1-8) clusters are recorded in the CH stretching region (2500-3100 cm-1). Spectra for the n = 1-3 clusters are interpreted with the aid of ab initio calculations at the MP2/6-311++G(2df 2p) level, which suggest that the CH4 ligands bind to F- by equivalent, linear hydrogen bonds. Anharmonic frequencies for CH4 and F--CH4 are determined using the vibrational self-consistent field method with second-order perturbation theory correction. The n = 1 complex is predicted to have a C3v structure with a single CH group hydrogen bonded to F-. Its spectrum exhibits a parallel band associated with a stretching vibration of the hydrogen-bonded CH group that is red-shifted by 380 cm-1 from the nu1 band of free CH4 and a perpendicular band associated with the asymmetric stretching motion of the nonbonded CH groups, slightly red-shifted from the nu3 band of free CH4. As n increases, additional vibrational bands appear as a result of Fermi resonances between the hydrogen-bonded CH stretching vibrational mode and the 2nu4 overtone and nu2+nu4 combination levels of the methane solvent molecules. For clusters with n < or = 8, it appears that the CH4 molecules are accommodated in the first solvation shell, each being attached to the F- anion by equivalent hydrogen bonds.     

Spectroscopy of OCS-hydrogen clusters in He droplets

Clusters of para-hydrogen (pH2) and ortho-deuterium (oD2) have been assembled around an OCS chromophore molecule inside He droplets in a molecular beam and studied via IR diode laser depletion spectroscopy (nu approximately 2060 cm-1). The superfluid 4He droplets provide a gentle host ensuring a constant low temperature of either T = 0.38 K for 4He droplets or T = 0.15 K for both the pure 3He and mixed 4He-3He droplets. The spectra show well resolved rotational structure of the vibrational bands for each attached hydrogen molecule in the range n = 1-8. With only one (n = 1) attached pH2, HD or an oD2 molecule the best fit rotational constants were used to determine the structure of the complex, which was found to be in surprisingly good agreement with quantum chemical calculations for the free complex. With n = 5 and 6 the Q-branch disappears for the pH2 clusters but not for the oD2 clusters which is consistent with a donut model. The moments of inertia of the pH2 and the oD2 complexes are explained by a new model in which each of the 18 attached helium atoms in a shell surrounding the OCS molecule are assigned a mass of 0.55, while each attached H2 and D2 molecule has an effective mass of about 10 and 12 u, respectively.     

IR spectroscopy of hydrogen-bonded 2-fluoropyridine-methanol clusters

The electronic and infrared spectra of 2-fluoropyridine-methanol clusters were observed in a supersonic free jet. The structure of hydrogen-bonded clusters of 2-fluoropyridine with methanol was studied on the basis of the molecular orbital calculations. The IR spectra of 2-fluoropyridine-(CH3OH)n(n = 1-3) clusters were observed with a fluorescence-detected infrared depletion (FDIR) technique in the OH and CH stretching vibrational regions. The structures of the clusters are similar to those observed for 2-fluoropyridine-(H2O)n (n = 1-3) clusters. The existence of weak hydrogen bond interaction through aromatic hydrogen was observed in the IR spectra. The theoretical calculation also supports the result. The vibrational frequencies of CH bonds in CH3 group are affected by hydrogen bond formation although these bonds do not directly relate to the hydrogen bond interaction. The B3LYP/6-311 ++G(d,p) calculations reproduce well the vibrational frequency of the hydrogen-bonded OH stretching vibrations. However, the calculated frequency of CH stretching vibration could not reproduce the IR spectra because of anharmonic interaction with closely lying overtone or combination bands for nu3 and nu9 vibrations. The vibrational shift of nu2 vibration is reproduced well with molecular orbital calculations. The calculation also shows that the frequency shift of nu2 vibration is closely related to the CH bond length at the trans position against the OH bond in hydrogen-bonded methanol.     

Infrared spectra of seeded hydrogen clusters: (para-H2)N-N2O and (ortho-H2)N-N2O, N = 2-13

High-resolution infrared spectra of clusters containing para-H2 and/or ortho-H2 and a single nitrous oxide molecule are studied in the 2225-cm(-1) region of the upsilon1 fundamental band of N2O. The clusters are formed in pulsed supersonic jet expansions from a cooled nozzle and probed using a tunable infrared diode laser spectrometer. The simple symmetric rotor-type spectra generally show no resolved K structure, with prominent Q-branch features for ortho-H2 but not para-H2 clusters. The observed vibrational shifts and rotational constants are reported. There is no obvious indication of superfluid effects for para-H2 clusters up to N=13. Sharp transitions due to even larger clusters are observed, but no definite assignments are possible. Mixed (para-H2)N-(ortho-H2)M-N2O cluster line positions can be well predicted by linear interpolation between the corresponding transitions of the pure clusters.     

Photogeneration of metastable side-on N2 linkage isomers in [Ru(NH3)5N2]Cl2, [Ru(NH3)5N2]Br2 and [Os(NH3)5N2]Cl2

Photogeneration of side-on N2 linkage isomers in [Ru(NH3)5N2]2+ and [Os(NH3)5N2]2+ is achieved by irradiation with lambda = 325 nm of powder samples at T = 80 K and detected by the downshift of the nu(N-N) vibration and by the heat release at elevated temperature due to the back switching of the side-on configuration to the ground state. The concentration of the transferred molecules is evaluated by the decrease of the area of the nu(N-N) or 2nu(N-N) vibrational bands. All characteristic changes between the linear Ru-N-N and side-on configuration are predicted by DFT calculations: the structure of the anion, shifts of the vibrations, electronic excitation energy, energetic position and sequence of the electronic orbitals, the potentials of the ground and relaxed metastable state with the activation energy, saddle points and energetic position of the minimum.     

Helium clusters seeded with CO molecules: new results for HeN-13C18O and the approach to the nanodroplet limit

Infrared spectra of helium clusters seeded with doubly substituted carbon monoxide molecules, 13C18O, have been studied in order to complement recent helium nanocluster results and to determine whether additional isotopic data would help to separate vibrational and rotational contributions to the observed transitions. The experiments were made by direct infrared absorption in pulsed supersonic jet expansions using a tunable diode laser probe in the region of the fundamental band (approximately 2045 cm-1 for 13C18O). Even with data on the R0 transitions from four CO isotopomers, it was found that a clear and consistent separation of vibration and rotation could not be achieved for HeN-CO clusters in the size range N approximately 10-20. Isotope shifts observed for clusters with 13C18O (relative to 12C16O) were found to be close to the sums of the shifts previously determined for 13C16O and 12C18O. The new measurements generally supported previous assignments of cluster size, but some modifications for the range N=14-16 are suggested here. New measurements for HeN-12C16O under conditions favoring larger clusters (high backing pressure and low jet temperature) showed that individual transitions could be resolved even at N approximately 50. For larger clusters, a partly resolved "lump" of transitions was observed to approach the nanodroplet limit.     

Infrared spectra of helium clusters seeded with nitrous oxide, 4HeN-N2O, with N=1-80

High resolution infrared spectra of HeN-N2O clusters are studied in the 2200 cm(-1) region of the N2O nu1 fundamental band. The clusters are produced in a pulsed supersonic jet expansion from a cooled nozzle source and probed using a tunable diode laser operating in a rapid-scan mode. Three isotopic forms are used (14N14N16O, 15N14N16O, and 15N15N16O) in order to support the spectral analyses. For clusters up to N approximately 24, the individual spectra are resolved, assigned, and analyzed together with complementary microwave data. Assignments for larger clusters are uncertain due to overlapping transitions, but an approximate analysis is still possible for N approximately 25-80. Compared to helium clusters containing the related CO2 or OCS molecules, the rotational dynamics of HeN-N2O clusters show similarities but also important differences. In particular, HeN-N2O has more irregular behavior in the range of N=6-17, indicating that conventional molecular structure plays a greater role. In general terms, these differences can be attributed to a greater degree of angular anisotropy in the He-N2O intermolecular potential.     

Fourier-transform infrared and Raman spectra,and ab initio calculations for cadmium-n-di-iso-propylphosphorylguanidine-di-chloride (CdDPGCl2) complex

Cadmium-n-di-isopropylphosphorylguanidine-di-chloride (CdDPGCl2) was synthesized in the solid phase and characterized previously. The Fourier transform infrared and Raman spectra of (CdDPGCl2) in the solid state were recorded and analyzed. Emphasis was placed on the vibrational assignment of the [(O2P=O-[CdCl2]-HN=C) fragment of the complete molecular structure. With the aim of assisting the vibrational assignment of the experimental spectra, a comparison with the spectra of N-di-isopropylphosphorylguanidine ligand was carried out and ab initio calculations have been performed with several effective core potentials and valence basis sets (Hay-Wadt (HW) and Stevens-Basch-Krauss (SBK)). Due to our limited computational resources, hydrogen atoms replaced the isopropyl groups. The calculated geometrical parameters showed excellent agreement with the experimental, as well as the RHF/MP2 calculated infrared wave numbers, when compared to the IR/Raman experimental wave numbers.     

A low-spin alkylperoxo-iron(III) complex with weak Fe-O and O-O bonds: implications for the mechanism of superoxide reductase

The synthesis of a mononuclear, five-coordinate ferrous complex [([15]aneN4)FeII(SPh)](BF4) (1) is reported. This complex is a new model of the reduced active site of the enzyme superoxide reductase (SOR), which is comprised of a [(NHis)4(Scys)FeII] center. Complex 1 reacts with alkylhydroperoxides (tBuOOH, cumenylOOH) at low temperature to give a metastable, dark red intermediate (2a: R = tBu; 2b: R = cumenyl) that has been characterized by UV-vis, EPR, and resonance Raman spectroscopy. The UV-vis spectrum (-80 degrees C) reveals a 526 nm absorbance (epsilon = 2150 M-1 cm-1) for 2a and a 527 nm absorbance (epsilon = 1650 M-1 cm-1) for 2b, indicative of alkylperoxo-to-iron(III) LMCT transitions, and the EPR data (77 K) show that both intermediates are low-spin iron(III) complexes (g = 2.20 and 1.97). Definitive identification of the Fe(III)-OOR species comes from RR spectra, which give nu(Fe-O) = 612 (2a) and 615 (2b) cm-1, and nu(O-O) = 803 (2a) and 795 (2b) cm-1. The assignments for 2a were confirmed by 18O substitution (tBu18O18OH), resulting in a 28 cm-1 downshift for nu(Fe-18O), and a 46 cm-1 downshift for nu(18O-18O). These data show that 2a and 2b are low-spin FeIII-OOR species with weak Fe-O bonds and suggest that a low-spin intermediate may occur in SOR, as opposed to previous proposals invoking high-spin intermediates.     

Vibrational spectra of Na, K, Mn2+, Ni2+ and Zn2+ salts of 1,2,4,5-benzenetetracarboxylic (pyromellitic) acid--a short hydrogen bond evidence

Five salts of 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), [C6H2(COO)4H4], have been synthesized and investigated by infrared and Raman spectroscopy and by single crystal X-ray diffraction methods: sodium salt [Na2(H2O)2][C6H2(COO)4H2], potassium salt [K(H2O)3][C6H2(COO)4H3] and transition metal salts [M(H2O)6][C6H2(COO)4H2], which M = Mn, Ni and Zn. Crystal structures of all five compounds show short intramolecular asymmetric hydrogen bonds (SHB) between adjacent carboxyl groups with O...O distance average of 2.40 A. The Raman and infrared spectra reported indicate the presence of short hydrogen bonds in all salts, in agreement with the X-ray data. The O-H stretching mode [nu(OH)] had been observed at about 2500 cm(-1). Deuterated analogues were synthesized and their Raman spectra show that nu(OH)/nu(OD) ratio average is about unit. The symmetric [nu(sym)(O..H..O)] and asymmetric [nu(asym)(O..H..O)] stretching modes have been attributed about 300 and 870 cm(-1), respectively, in all salts, and for deuterated analogues, the ratio nu(OH)/nu(OD) to nu(sym)(O..H..O, O..D..O) is close to unit like it occurs in nu(OH). The vibrational modes, mainly SHB modes, are tentatively assigned by molecular orbital ab initio calculations of pyromellitic acid and anions [C6H2(COO)4H3]- and [C6H2(COO)4H2]2-. Geometry optimizations showed a good agreement with experimental data. Frequency calculation confirms the assignment of specific vibrational modes. Ab initio calculations show that nu(C=O) and nu(sym)(COO) are strongly coupled with in plane OH bending [delta(OH)]. In Raman spectra of deuterated analogues is observed a frequency shift of these bands.     

Dioxygen reactivity of a copper(I) complex with a N3S thioether chelate; peroxo-dicopper(II) formation including sulfur-ligation

Employing a tetradentate N3S(thioether) ligand, LN3S, dioxygen reactivity of a copper(I) complex, [(LN3S)CuI]+ (1) was examined. In CH2Cl2, acetone (at -80 degrees C), or 2-methyltetrahydrofuran (at -128 degrees C), 1 reacts with O2 producing the end-on bound peroxodicopper(II) complex [{(LN3S)CuII}2(mu-1,2-O2(2-))]2+ (2), the first reported copper-dioxygen adduct with sulfur (thioether) ligation. Its absorption spectrum contains an additional low-energy feature (but not a Cu-S CT band) compared to the previously well-characterized N4 ligand complex, [{(TMPA)CuII}2(mu-1,2-O2(2-))]2+ (3) (TMPA = tris(2-pyridylmethyl)amine). Resonance Raman spectroscopy confirms the peroxo formulation {nu(O-O) = 817 cm-1 (16-18O2 Delta = 46 cm-1) and nu(Cu-O) = 545 cm-1 (16-18O2 Delta = 26 cm-1), in close analogy to that known for 3 {nu(O-O) = 827 cm-1 and nu(Cu-O) = 561 cm-1}. Direct evidence for thioether ligation comes from EXAFS spectroscopy {Cu K-edge; Cu-S = 2.4 A}.     

Study of NH stretching vibrations in small ammonia clusters by infrared spectroscopy in He droplets and ab initio calculations

Infrared spectra of the NH stretching vibrations of (NH3)n clusters (n = 2-4) have been obtained using the helium droplet isolation technique and first principles electronic structure anharmonic calculations. The measured spectra exhibit well-resolved bands, which have been assigned to the nu1, nu3, and 2nu4 modes of the ammonia fragments in the clusters. The formation of a hydrogen bond in ammonia dimers leads to an increase of the infrared intensity by about a factor of 4. In the larger clusters the infrared intensity per hydrogen bond is close to that found in dimers and approaches the value in the NH3 crystal. The intensity of the 2nu4 overtone band in the trimer and tetramer increases by a factor of 10 relative to that in the monomer and dimer, and is comparable to the intensity of the nu1 and nu3 fundamental bands in larger clusters. This indicates the onset of the strong anharmonic coupling of the 2nu4 and nu1 modes in larger clusters. The experimental assignments are compared to the ones obtained from first principles electronic structure anharmonic calculations for the dimer and trimer clusters. The anharmonic calculations were performed at the M?ller-Plesset (MP2) level of electronic structure theory and were based on a second-order perturbative evaluation of rovibrational parameters and their effects on the vibrational spectra and average structures. In general, there is excellent (<20 cm(-1)) agreement between the experimentally measured band origins for the N-H stretching frequencies and the calculated anharmonic vibrational frequencies. However, the calculations were found to overestimate the infrared intensities in clusters by about a factor of 4.     

High-resolution infrared spectroscopy in the 1,200-1,300 cm(-1) region and accurate theoretical estimates for the structure and ring-puckering barrier of perfluorocyclobutane

We present experimental infrared spectra and theoretical electronic structure results for the geometry, anharmonic vibrational frequencies, and accurate estimates of the magnitude and the origin of the ring-puckering barrier in C4F8. High-resolution (0.0015 cm-1) spectra of the nu12 and nu13 parallel bands of perfluorocyclobutane (c-C4F8) were recorded for the first time by expanding a 10% c-C4F8 in helium mixture in a supersonic jet. Both bands are observed to be rotationally resolved in a jet with a rotational temperature of 15 K. The nu12 mode has b2 symmetry under D2d that correlates to a2u symmetry under D4h and consequently has +/- <-- +/- ring-puckering selection rules. A rigid rotor fit of the nu12 band yields the origin at 1292.56031(2) cm-1 with B' = 0.0354137(3) cm-1 and B' ' = 0.0354363(3) cm-1. The nu13 mode is of b2 symmetry under D2d that correlates to b2g under D4h, and in this case, the ring-puckering selection rules are +/- <-- -/+ . Rotational transitions from the ground and first excited torsional states will be separated by the torsional splitting in the ground and excited vibrational states, and indeed, we observe a splitting of each transition into strong and weak intensity components with a separation of approximately 0.0018 cm-1. The strong and weak sets of transitions were fit separately again using a rigid rotor model to give nu13(strong) = 1240.34858(4) cm-1, B' = 0.0354192(7) cm-1, and B' ' = 0.0354355(7) cm-1 and nu13(weak) = 1240.34674(5) cm-1, B' = 0.0354188(9) cm-1, and B' ' = 0.0354360(7) cm-1. High-level electronic structure calculations at the MP2 and CCSD(T) levels of theory with the family of correlation consistent basis sets of quadruple-zeta quality, developed by Dunning and co-workers, yield best estimates for the vibrationally averaged structural parameters r(C-C) = 1.568 A, r(C-F)alpha = 1.340 A, r(C-F)beta = 1.329 A, alpha(F-C-F) = 110.3 degrees , thetaz(C-C-C) = 89.1 degrees , and delta(C-C-C-C) = 14.6 degrees and rotational constants of A = B = 0.03543 cm-1 and C = 0.02898 cm-1, the latter within 0.00002 cm-1 from the experimentally determined values. Anharmonic vibrational frequencies computed using higher energy derivatives at the MP2 level of theory are all within <27 cm-1 (in most cases <5 cm-1) from the experimentally measured fundamentals. Our best estimate for the ring-puckering barrier at the CCSD(T)/CBS (complete basis set) limit is 132 cm-1. Analysis of the C4F8 electron density suggests that the puckering barrier arises principally from the sigmaCC-->sigmaCF hyperconjugative interactions that are more strongly stabilizing in the puckered than in the planar form. These interactions are, however, somewhat weaker in C4F8 than in C4H8, a fact that is consistent with the smaller barrier in the former (132 cm-1) with respect to the latter (498 cm-1).     

Electronic and resonance Raman spectra of [Au2(CS3)2]2-. Spectroscopic properties of a "short" Au(I)-Au(I) bond

The anion [Au2(CS3)2]2- has an unusually short Au-Au distance (2.80 A) for a binuclear Au(I) complex. We report detailed Raman studies of the nBu4N+ salt of this complex, including FT-Raman of the solid and UV/vis resonance Raman of dimethyl sulfoxide solutions. All five totally symmetric vibrations of the anion have been located and assigned. A band at delta nu = 125 cm-1 is assigned to nu (Au2). The visible-region electronic absorption bands (384 (epsilon 30,680) and 472 nm (epsilon 610 M-1 cm-1)) are attributable to CS3(2-) localized transitions, as confirmed by the dominance of nu sym(C-Sexo) (delta nu = 951 cm-1) in RR spectra measured in this region. An absorption band at 314 nm (22,250 M-1 cm-1) is assigned as the metal-metal 1(d sigma*-->p sigma) transition, largely because nu sym(C-Sexo) is not strongly enhanced in RR involving this band. Observation of the expected strong resonance enhancement of nu (Au2) was precluded as a result of masking by intense solvent Rayleigh scattering in the UV.     

Infrared spectra of CO2-doped 4He clusters, 4HeN-CO2, with N=1-60

High resolution spectra of (4)He(N)-CO(2) clusters are studied in the region of the CO(2) nu(3) fundamental band (approximately 2300 cm(-1)). The clusters are produced in a pulsed supersonic jet expansion from a cooled nozzle source and probed by direct absorption using a tunable diode laser operating in a rapid-scan mode. Four carbon dioxide isotopes ((16)O(12)C(16)O, (16)O(13)C(16)O, (18)O(13)C(18)O, and (16)O(13)C(18)O) are used to support the analysis, and because additional rotational transitions are allowed for the asymmetric one ((16)O(13)C(18)O). Resolved R(0) (J=1<--0) rotation-vibration transitions are observed for clusters up to N=60. A detailed rotational analysis is possible up to N approximately 20 and, with some assumptions, to N approximately 37 and beyond. The derived rotational constants (B values) vary smoothly with N and show evidence for broad oscillations similar to those already reported for He(N)-OCS and He(N)-N(2)O. Possible indications of a disruption are observed in the J=2 levels of larger clusters (N>22) which could be caused by interactions with a "dark" helium cluster modes.     

Crystal field splitting of rovibrational transitions of water monomers isolated in solid parahydrogen

We report polarized infrared absorption spectra of water isotopologues isolated in solid parahydrogen (pH2) which reveal the crystal field induced splittings of the 1 01<--0 00 R(0) lines in the nu1 HDO, nu3 D2O, nu3 HDO, and nu3 H2O fundamental bands. For annealed pH2 solids, these spectra also reveal a strong alignment of the hexagonal-close-packed crystallites' c axes with the deposition substrate surface normal. This alignment effect explains our failure to detect the parallel-polarized components of these R(0) lines in spectra of pH2 solids produced on a transparent deposition substrate [M. E. Fajardo et al., J. Mol. Struct. 695, 111 (2004)]. This lesson applies more generally to comparison of solid pH2 spectra obtained in different laboratories. The spectra are consistent with water monomers existing in solid pH2 as very slightly hindered rotors. The individual components of the R(0) absorption lines show a Lorentzian lineshape, with vibrational depopulation the most important source of line broadening.     

Infrared evidence of NO linkage photoisomerization in Na2[Fe(CN)5NO].2H2O at low temperature: experimental and theoretical (DFT) isotopic shifts from 15n(O), 18O and 54Fe species

Infrared spectra of the metastable state I (MSI) of normal and 15NO, N18O and 54Fe isotopically substituted sodium nitroprusside dihydrate (Na2[Fe(CN)5NO].2H2O) have been obtained at 77 K. A comparison of the isotopic shifts measured for the vibrational modes of the FeXY (XY = NO or ON) moiety with those calculated by means of quantum chemistry (DFT) procedures supports the linear Fe-O = N arrangement for the MSI state.     

Ab initio calculations of anharmonic vibrational spectroscopy for hydrogen fluoride (HF)n (n = 3, 4) and mixed hydrogen fluoride/water (HF)n(H2O)n (n = 1, 2, 4) clusters

Anharmonic vibrational frequencies and intensities are computed for hydrogen fluoride clusters (HF)n, with n = 3, 4 and mixed clusters of hydrogen fluoride with water (HF)n(H2O)n where n = 1, 2. For the (HF)4(H2O)4 complex, the vibrational spectra are calculated at the harmonic level, and anharmonic effects are estimated. Potential energy surfaces for these systems are obtained at the MP2/TZP level of electronic structure theory. Vibrational states are calculated from the potential surface points using the correlation-corrected vibrational self-consistent field method. The method accounts for the anharmonicities and couplings between all vibrational modes and provides fairly accurate anharmonic vibrational spectra that can be directly compared with experimental results without a need for empirical scaling. For (HF)n, good agreement is found with experimental data. This agreement shows that the M?ller-Plesset (MP2) potential surfaces for these systems are reasonably reliable. The accuracy is best for the stiff intramolecular modes, which indicates the validity of MP2 in describing coupling between intramolecular and intermolecular degrees of freedom. For (HF)n(H2O)n experimental results are unavailable. The computed intramolecular frequencies show a strong dependence on cluster size. Intensity features are predicted for future experiments.