Ν4 Bending Modes Research Articles

The single-crystal, polarized-light, FTIR spectrum of stoppaniite, the Fe analogue of beryl

We report here a single-crystal polarized-light study of stoppaniite, ideally (Fe,Al,Mg)4(Be6Si12O36)(H2O)2(Na,□), from Capranica (Viterbo). Polarized-light FTIR spectra were collected on an oriented (hk0) section, doubly polished to 15 μm. The spectrum shows two main bands at 3,660 and 3,595 cm−1; the former is strongly polarized for E ⊥c, while the latter is polarized for E //c. A sharp and very intense band at 1,620 cm−1, plus minor features at 4,000 and 3,228 cm−1 are also polarized for E //c. On the basis of literature data and considering the pleochroic behavior of the absorptions, the 3,660 cm−1 band is assigned to the ν3 stretching mode and the 1,620 cm−1 (associated with an overtone 2*ν2 at 3,230 cm−1) band to the ν2 bending mode of “type II” water molecules within the structural channels of the studied beryl. The sharp band at 3,595 cm−1 is not associated with a corresponding ν2 bending mode; thus it is assigned to the stretching vibration of O–H groups in the sample. The minor 4,000 cm−1 feature can be assigned to the combination of the O–H bond parallel to c with a low-frequency metal-oxygen mode such as the Na–O stretching mode. The present results suggest that the interpretation of the FTIR spectrum of Na-rich beryl needs to be carefully reconsidered.

Low-lying bending vibronic bands of the MgNC ÃΠ2−X̃Σ+2 transition

We have generated MgNC in supersonic free jet expansions and measured the laser induced fluorescence excitation spectra of the Mg-N-C bending vibronic bands of the A 2Pi-X 2Sigma+ transition. In addition to the two vibronic bands, 2(0) (1), kappa 2Sigma(+)- and 2(0) (2), kappa 2Pi-2Sigma+, reported previously, the 2(0) (2), mu 2Pi1/2-(2)Sigma+ vibronic subband was found just above the 2(0) (1) band. The most remarkable feature of this subband is unexpected rotational structure of the A (020) mu 2Pi1/2 level, showing the splitting of the e and f sublevels. On the basis of the fact that the A (020) mu 2Pi1/2 level lies very close to the A (010) kappa2Sigma+ level, the ef splitting is ascribed to P-type doubling which is induced by Coriolis interaction between these two bending vibronic levels. Introducing the Coriolis coupling terms arising from the G-uncoupling operator, -J+/-G22-/+, and the spin-Coriolis interaction, S+/-G22-/+, into the rotational Hamiltonian, this unexpected rotational structure has been analyzed. This P-type doubling would be one of the rare examples exhibiting the Coriolis interaction between two bending vibronic levels with Deltav2=+/-1 and Deltal=-/+1. Through the molecular constants of the A (010) kappa 2Sigma+, (020) kappa 2Pi, and mu 2Pi1/2 levels, the Renner-Teller vibronic structure of the nu2 bending mode in the A 2Pi state has been characterized. The observed vibronic bands analyzed in this study show some anomalies in the band intensities. Based on the information of the nu2 bending vibronic structure derived from the present analyses, we discuss the intensity anomalies.

Observation of the ν3 Raman band of S3− inserted into sodalite cages

AbstractThe S3− radical anion is observed in several systems: non‐aqueous polysulfides solutions, doped alkali halides, ultramarine pigments (UP) for which S3− is the blue chromophore and S2− is the yellow one and pigments of zeolite 4A structure. The S3− ion has C2V symmetry, and therefore its three vibrational modes should be observed in the Raman and in IR spectra. In resonance Raman spectroscopy, only the symmetric stretching mode ν1 and the bending mode ν2 have been observed, whereas the anti‐symmetric stretching mode ν3 has never been observed whatever the system. In this work, we confirm that ν3 is not observed in solutions with resonance Raman spectroscopy. However, our investigation of several blue UP, with various concentrations of S2−, shows that there is a superposition of two bands at ca 590 cm−1: the first is assigned to ν (S2−) and the second to ν3 (S3−). With the 457.9 nm excitation line, for which the resonance conditions are simultaneously fulfilled for S2− and S3−, the band at ca 590 cm−1 is the sum of the contributions of both ν (S2−) and ν3 (S3−) vibrations, while, with the 647.1 nm line, which only satisfies the resonance conditions of S3−, the band at ca 584 cm−1 must be assigned only to ν3 (S3−). Furthermore, ν3 (S3−) is observed in green UP and in pigments of zeolite structure. The ν3 vibration of S3−, which is observed neither in polysulfide solutions nor in doped alkali halides in resonance Raman conditions, can therefore be observed when this species is inserted into the β‐cages of the sodalite or of the zeolite 4A structures. So, the band at ca 590 cm−1 cannot always be assigned to S2− in these systems. This implies that the concentration of S2− in UP must be reconsidered. Copyright © 2007 John Wiley & Sons, Ltd.

Raman spectroscopy of the borosilicate mineral ferroaxinite

AbstractRaman spectroscopy, complemented by infrared spectroscopy, has been used to characterise the ferroaxinite minerals of the theoretical formula Ca2Fe2+Al2BSi4O15(OH), a ferrous aluminium borosilicate. The Raman spectra are complex but are subdivided into sections on the basis of the vibrating units. The Raman spectra are interpreted in terms of the addition of borate and silicate spectra. Three characteristic bands of ferroaxinite are observed at 1082, 1056 and 1025 cm−1 and are attributed to BO4 stretching vibrations. Bands at 1003, 991, 980 and 963 cm−1 are assigned to SiO4 stretching vibrations. Bands are found in these positions for each of the ferroaxinites studied. No Raman bands were found above 1100 cm−1 showing that ferroaxinites contain only tetrahedral boron. The hydroxyl stretching region of ferroaxinites is characterised by a single Raman band between 3368 and 3376 cm−1, the position of which is sample‐dependent. Bands for ferroaxinite at 678, 643, 618, 609, 588, 572, 546 cm−1 may be attributed to the ν4 bending modes and the three bands at 484, 444 and 428 cm−1 may be attributed to the ν2 bending modes of the (SiO4)2−. Copyright © 2006 John Wiley & Sons, Ltd.

Characterization and electrical properties of methyl‐2‐hydroxyethyl cellulose doped with erbium nitrate salt

AbstractX‐ray diffraction, infrared (IR), and electrical properties for pure and Er (NO3)3‐doped methyl‐2‐hydroxyethyl cellulose (MHEC) with concentrations of 0.5, 1, 2, 5, 7, and 10 wt % were studied. X‐ray analysis indicates that the addition of Er (NO3)3, which is a crystalline material, to MHEC at concentrations 10 and 13 wt % leads to the formation of crystalline phases in the amorphous polymeric matrix. The appearance of the bending mode ν2 and the combination mode (ν1 + ν4) of Er (NO3)3 in the IR spectra of composite samples indicates the coordination of nitro group in the chains of MHEC. From the I–V characteristics, it was found that the charge transport mechanism in MHEC appears to be essentially space charge limited conduction, while the predominant mechanism in the composite samples is Poole–Frenkel. Values of both drift mobility (μ) and the charge carrier density (n) has been reported. The temperature dependence conductivity data has been analyzed in terms of the Arrhenius and Mott's variable range hopping models. Different Mott's parameters such as the density of states, N(EF), hopping distance (R), and average hopping energy (W) have been evaluated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:2352–2361, 2006

A Raman spectroscopic study of selected minerals of the rosasite group

AbstractMinerals in the rosasite mineral group, namely, rosasite, glaukosphaerite, kolwezite, mcguinnessite, nullaginite and pokrovskite have been studied by Raman spectroscopy at 298 and 77 K, complemented with infrared spectroscopy. The spectral patterns for the minerals rosasite, glaukosphaerite, kolwezite and mcguinnessite are similar to those of malachite, implying that the structure is the same as that of malachite, i.e. monoclinic. A comparison is made with the spectra of malachite. The symmetry of the carbonate anion in the rosasite mineral group is C2v or Cs and is composition dependent. Two (CO3)2− symmetric stretching modes are observed for the rosasite minerals at 1060 and 1090 cm−1. Two hydroxyl stretching modes are observed for the rosasite mineral group. The position of these bands is determined to be a function of the hydrogen bond lengths. Hydrogen bond distances for rosasite are calculated as 2.867, 2.799 and 2.780 Å, whereas for pokrovskite the distances are 3.280 and 2.999 Å. The effect of lowering the temperature from ambient to 77 K results in a decrease of the hydrogen bond distances by 5%. Multiple Raman bands are observed in the 800 to 850 cm−1 and the 720 to 750 cm−1 regions and are attributed to ν2 and ν4 bending modes confirming the reduction of the carbonate anion in the rosasite structure. Copyright © 2006 John Wiley & Sons, Ltd.

Raman spectroscopy of uranyl rare earth carbonate kamotoite-(Y)

Raman spectroscopy at 298 and 77K has been used to study the mineral kamotoite-(Y), a uranyl rare earth carbonate mineral of formula Y2(UO2)4(CO3)3(OH)8·10–11H2O. The mineral is characterised by two Raman bands at 1130.9 and 1124.6cm−1 assigned to the ν1 symmetric stretching mode of the (CO3)2− units, while those at 1170.4 and 862.3cm−1 (77K) to the δU–OH bending vibrations. The assignment of the two bands at 814.7 and 809.6cm−1 is difficult because of the potential overlap between the symmetric stretching modes of the (UO2)2+ units and the ν2 bending modes of the (CO3)2− units. Only a single band is observed in the 77K spectrum at 811.6cm−1. One possible assignment is that the band at 814.7cm−1 is attributable to the ν1 symmetric stretching mode of the (UO2)2+ units and the second band at 809.6cm−1 is due to the ν2 bending modes of the (CO3)2− units. Bands observed at 584 and 547.3cm−1 are attributed to water librational modes. An intense band at 417.7cm−1 resolved into two components at 422.0 and 416.6cm−1 in the 77K spectrum is assigned to an Y2O2 stretching vibration. Bands at 336.3, 286.4 and 231.6cm−1 are assigned to the ν2 (UO2)2+ bending modes. U–O bond lengths in uranyl are calculated from the wavenumbers of the uranyl symmetric stretching vibrations. The presence of symmetrically distinct uranyl and carbonate units in the crystal structure of kamotoite-(Y) is assumed. Hydrogen-bonding network related to the presence of water molecules and hydroxyls is shortly discussed.

Six-Dimensional Potential Energy Surface and Rovibrational Energies of the HCCN Radical in the Ground Electronic State

We report large-scale quantum mechanical calculations for the HCCN radical in its ground electronic state. A six-dimensional potential energy surface based on MR-ACPF/cc-pVQZ ab initio energy points is developed and adjusted to reproduce experimental findings for and nu1 of HCCN. Rovibrational energy levels of HCCN and DCCN are computed for total rotational angular momentum J = 0-4 by making use of combined (functional + point wise) coordinate representations together with contraction schemes resulting from several diagonalization/truncation steps. The classical barrier to linearity is determined to be 287 cm(-1). Spectroscopic parameters are calculated for low lying states and compared with available experimental data. Energy patterns attributed to the nu4 bending mode and to the quasilinear nu5 bending mode are identified. It has been also found that nu2 and nu3 + (nu4(1),nu5(1))(0,0) are coupled in HCCN, while the mixing between nu3 and (2nu4(0), 2nu5(0))(0,0) is seen in DCCN.

Quasiclassical trajectory calculations comparing the reactivity and dynamics of symmetric and asymmetric stretch and the role of the bending mode excitations of methane in the Cl+CH4 reaction

To analyze the effects of the symmetric (nu(1)) and asymmetric (nu(3)) stretch mode excitations and the role played by the "umbrella" bending (nu(4)) mode excitation in the reactivity and the dynamics of the gas-phase Cl+CH(4) reaction, an exhaustive dynamics study was performed. Quasiclassical trajectory (QCT) calculations, including corrections to avoid zero-point energy leakage along the trajectories, were used in this work on an analytical potential energy surface previously developed by Espinosa-Garcia et al. [J. Chem. Phys. (to be published)]. First, with respect to the reactivity, we found that the nu(1) mode excitation is more reactive than the nu(3) mode by a factor of 1.20, in agreement with the experimental tendency between these modes. The inclusion of the nu(4) bending mode practically does not affect this relative reactivity, (nu(1+)nu(4))(nu(3+)nu(4)) = 1.16. Second, with respect to the dynamics (rotovibrational and angular distributions of the products), the two stretch modes, nu(1) and nu(3), give very similar pictures, reproducing the experimental behavior, and the nu(4) "umbrella" mode does not affect the dynamics. The satisfactory reproduction (always qualitatively acceptable and sometimes even quantitatively) of a great variety of experimental data by the QCT study presented here lends confidence to the potential energy surface constructed by Espinosa-Garcia et al. [J. Chem. Phys. (to be published)].

Raman spectroscopy of three polymorphs of BiVO4: clinobisvanite, dreyerite and pucherite, with comparisons to (VO4)3‐bearing minerals: namibite, pottsite and schumacherite

AbstractBoth Raman and infrared spectroscopy have been used to characterise the three phase‐related minerals—dreyerite (tetragonal BiVO4), pucherite (orthorhombic BiVO4) and clinobisvanite (monoclinic BiVO4)—and a comparison of the spectra is made with that of the minerals namibite (Cu(BiO2)VO4(OH)), schumacherite (Bi3O(OH)(VO4)2) and pottsite (PbBiH(VO4)2·2H2O). Pucherite, clinobisvanite and namibite are characterised by VO4 stretching vibrations at 872, 824 and 846 cm−1. The Raman spectrum of dreyerite shows complexity in the 750 to 950 cm−1 region with two intense bands at 836 and 790 cm−1 assigned to the symmetric and antisymmetric VO4 modes. The minerals schumacherite and pottsite are characterised by bands at 846 and 874 cm−1. In both the infrared and Raman, spectra bands are observed in the 1000–1100 cm−1 region which are attributed to the antisymmetric stretching modes. The Raman spectra of the low wavenumber region are complex. Bands are identified in the 328 to 370 cm−1 region and in the 404 to 498 cm−1 region and are assigned to the ν2 and ν4 bending modes. The minerals namibite and schumacherite are characterised by intense bands at 3514 and 3589 cm−1 assigned to the symmetric stretching vibrations of the OH units. Importantly, Raman spectroscopy enables new insights into the chemistry of these bismuth vanadate minerals. Raman spectroscopy enables the identification of the bismuth vanadate minerals in mineral matrices where paragenetic relationships exist between the minerals. Copyright © 2006 John Wiley & Sons, Ltd.

Raman spectroscopy of beaverite and plumbojarosite

AbstractRaman spectroscopy has been used to characterise the compound of formula Pb(Fe3+, Cu2+)3(SO4)2(OH)6, equivalent to synthetic beaverite, one of the jarosite subgroup minerals. The mineral is characterised by multiple OH stretching vibrations attributed to non‐equivalent OH units in the structure. Multiple vibrations are observed for the SO42− stretching vibrations indicating the non‐equivalence of the sulphate units in the structure. This multiplicity is also reflected in the ν2 and ν4 bending modes. The Raman spectrum of beaverite is significantly different from that of plumbojarosite, for which multiple bands are not observed. Copyright © 2005 John Wiley & Sons, Ltd.

Using Raman spectroscopy to identify mixite minerals

Raman spectroscopy has been used to identify whether or not a selection of minerals labelled as mixites (formula BiCu6(AsO4)3(OH)6·3H2O) are correctly marked. Of the four samples, two samples are shown to be potentially mixites because of the presence of the characteristic Raman spectra of (AsO4)3− units and (HAsO4)− units, characterised by bands at around 803 and 833cm−1. Two of the minerals are shown to be predominantly carbonates. Bands are observed at 3473.9 and 3470.3cm−1 for the two mixite samples. Bands observed in the region 880–910cm−1 and in the 867–870cm−1 region are assigned to the AsO stretching vibrations of (HAsO4)2− and (H2AsO4)− units. Whilst bands at around 803 and 833cm−1 are assigned to the stretching vibrations of uncomplexed (AsO4)3− units. Intense bands observed at 473.7 and 475.4cm−1 are assigned to the ν4 bending mode of AsO4 units. Bands observed at around 386.5, 395.3 and 423.1cm−1 are assigned to the ν2 bending modes of the HAsO4 (434 and 400cm−1) and the AsO4 groups (324cm−1). Raman spectroscopy lends itself to the identification of minerals on host matrices and is especially useful for the identification of mixites.

THEORETICAL TRANSITION PROBABILITIES FOR THE $\tilde{A}^{2}A_{1} -\tilde{X}^{2}B_{1}$ SYSTEM OF H2O+ AND D2O+ AND RELATED FRANCK–CONDON FACTORS BASED ON GLOBAL POTENTIAL ENERGY SURFACES

To elucidate the ionization dynamics, in particular the vibrational distribution, of H 2 O +(Ã) produced by photoionization and the Penning ionization of H 2 O and D 2 O with He *(2 3S) atoms, Franck–Condon factors (FCFs) were given for the [Formula: see text] ionization, and the transition probabilities were presented for the [Formula: see text] emission. The FCFs were obtained by quantum vibrational calculations using the three-dimensional potential energy surfaces (PESs) of [Formula: see text] and [Formula: see text] electronic states. The global PESs were determined by the multi-reference configuration interaction calculations with the Davidson correction and the interpolant moving least squares method combined with the Shepard interpolation. The obtained FCFs exhibit that the [Formula: see text] state primarily populates the vibrational ground state, as its equilibrium geometry is almost equal to that of [Formula: see text], while the bending mode (ν2) is strongly enhanced for the H 2 O +(Ã) state; the maximums in the population of H 2 O + and D 2 O + are approximately v2 = 11–12 and 15–17, respectively. These results are consistent with the distributions observed by photoelectron spectroscopy. Transition probabilities for the [Formula: see text] system of H 2 O + and D 2 O + show that the bending progressions consist primarily of the [Formula: see text] emission, with combination bands from the (1, v′2 = 4–8, 0) level being next most important.

Feshbach resonances of the C3H− anion: laser autodetachment spectroscopy and ab initio calculations

The electronic spectra of the C3H− and C3D− anions have been studied above the lowest electron detachment threshold. On the basis of the vibrational, rotational analysis and ab initio calculations, the photodetachment spectrum is assigned to the d3 A″←a3 A″ Feshbach resonance in the bent chain C3H(D)− anion. The vibronic system is characterized by a long vibrational progression involving the CCH in plane bending mode ν4. The potential curves along this coordinate obtained from the spectral analysis and theoretical calculations reveal the importance of vibronic coupling in the electronic excited states. A strong Renner–Teller effect is thought to be the reason for the existence of the Feshbach resonance because the 4Σ− neutral parent and the 3Π anion excited states are close in energy. As for the neutral, ν4 appears to be the active mode and drives the interaction between the Feshbach and the dipole bound states.

Microcanonical unimolecular rate theory at surfaces. II. Vibrational state resolved dissociative chemisorption of methane on Ni(100).

A three-parameter microcanonical theory of gas-surface reactivity is used to investigate the dissociative chemisorption of methane impinging on a Ni(100) surface. Assuming an apparent threshold energy for dissociative chemisorption of E(0)=65 kJ/mol, contributions to the dissociative sticking coefficient from individual methane vibrational states are calculated: (i) as a function of molecular translational energy to model nonequilibrium molecular beam experiments and (ii) as a function of temperature to model thermal equilibrium mbar pressure bulb experiments. Under fairly typical molecular beam conditions (e.g., E(t)>/=25 kJ mol(-1), T(s)>/=475 K, T(n)</=400 K), sticking from methane in the ground vibrational state dominates the overall sticking. In contrast, under thermal equilibrium conditions at temperatures T>/=100 K the dissociative sticking is dominated by methane in vibrationally excited states, particularly those involving excitation of the nu(4) bending mode. Fractional energy uptakes f(j) defined as the fraction of the mean energy of the reacting gas-surface collision complexes that derives from specific degrees of freedom of the reactants (i.e., molecular translation, rotation, vibration, and surface) are calculated for thermal dissociative chemisorption. At 500 K, the fractional energy uptakes are calculated to be f(t)=14%, f(r)=21%, f(v)=40%, and f(s)=25%. Over the temperature range from 500 K to 1500 K relevant to thermal catalysis, the incident gas-phase molecules supply the preponderance of energy used to surmount the barrier to dissociative chemisorption, f(g)=f(t)+f(r)+f(v) approximately 75%, with the highest energy uptake always coming from the molecular vibrational degrees of freedom. The predictions of the statistical, mode-nonspecific microcanonical theory are compared to those of other dynamical theories and to recent experimental data.

Raman spectroscopic detection of wyartite in the presence of rabejacite

AbstractRaman microscopy was used to confirm the presence of wyartite, CaU5+(UO2)2(CO3)O4(OH)(H2O)7, in the presence of rabejacite, (Ca(UO2)4(SO4)2(OH)5·6H2O), obtained from the Ranger Mine, Northern Territory, Australia. This occurrence is unusual in that it means that a uranyl carbonate has been formed under acidic conditions. Wyartite is a mineral known for the occurrence of pentavalent U5+. A band is observed at 818 cm−1 in the Raman spectrum of wyartite assigned to the ν2 symmetric bending mode of the (CO3)2− units. The presence of carbonate is confirmed by the ν1 stretching vibration at 1071 cm−1 and the ν3 stretching vibrations at 1445 and 1345 cm−1. Two bands are observed at 853 and 837 cm−1 and are assigned to the ν1 stretching modes of the UO2 units. Raman spectroscopy allows the partial band separation of the ν2 (CO3)2− and ν1 modes of UO2. The Raman spectrum of rabejacite is characterized by an intense sharp band at 1010 cm−1 assigned to the ν1 stretching mode of (SO4)2−. Three bands observed at 1086, 1123 and 1175 cm−1 are attributed to the ν3 antisymmetric stretching modes of (SO4)2−. The mineral rabejacite is also characterized by ν2 bending modes at 457 and 394 cm−1 and ν4 bending modes at 666, 605, 537 and 505 cm−1. Raman spectroscopy has proven most useful for the detection of wyartite in the presence of other mineral phases. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Single‐crystal Raman study of erythrite, Co3(AsO4)2·8H2O

AbstractSingle‐crystal Raman and infrared spectra of natural and synthetic erythrite, Co3(AsO4)2·8H2O, are reported and compared with the spectra polycrystalline, synthetic annabergite, Ni3(AsO4)2·8H2O, and hörnesite, Mg3(AsO4)2·8H2O. Factor group analysis and single‐crystal considerations were used to interpret the experimental data. The Raman spectra of erythrite reveal the ν1 arsenate stretching vibration at 850 cm−1 (Ag) with the corresponding infrared band at 821 cm−1 (Bu). The ν3 antisymmetric vibration is split into three components, observed at 796 (Ag), 788 (Ag) and 803 (Bg) cm−1. The ν2 symmetric bending modes are observed at 375 (Ag) and 385 (Bg) cm−1. The ν4 bending modes are predicted to split into three bands which are observed at 441 (Ag), 446 (Bg) and 457 (Ag) cm−1. Lattice vibrations are found at 112 (Ag), 124 (Bg), 145 (Ag), 157 (Bg), 165 (Ag), 179 (Ag), 189 (Ag), 191 (Bg), 201 (Bg), 210 (Ag), 227 (Ag), 250 (Ag), 264 (Ag), 264 (Ag), 280 (Bg), 302 (Bg), 321 (Bg) and 338 cm−1(Ag). Hydroxyl stretching modes are observed at 3050, 3218, 3333, 3449 and 3479 cm−1 in the infrared spectrum. Raman‐active hydroxyl bands are detected at 3009 (Bg), 3052 (Ag), 3190 (Bg) 3203 (Bg), 3281 (Ag) and 3310 (Bg), 3436 (Bg) and 3443 (Ag) cm−1. Infrared hydroxyl bands at 3050 and 3218 cm−1 are from water type II, short hydrogen bonding distances, and the bands at 3449 and 3479 cm−1 are due to water I, long hydrogen bonding distances. Water bending modes are detected in the infrared spectrum at 1571, 1621, 1641 and 1682 cm−1, but owing to the inherent weak Raman scattering cross‐section of water these could not be detected in the Raman spectra. Copyright © 2004 John Wiley &amp; Sons, Ltd.

He * (2 3 S) Penning ionization of H2S. I. Theoretical Franck–Condon factors for the H2S(X̃ 1A1,v′=0)→H2S+(X̃ 2B1,à 2A1) ionization and H2S+(ÖX̃) transition

In order to elucidate the ionization dynamics, in particular the vibrational distribution, of H2S+(Ã) produced by the Penning ionization of H2S with He*(2 3S) atoms, the Franck–Condon factors (FCFs) were presented for the H2S(X̃)→H2S+(X̃,Ã) ionization and the H2S+(ÖX̃) transition, and Einstein’s A coefficients were presented for the latter transition. The FCFs were obtained by quantum vibrational calculations using the global potential energy surfaces (PESs) of H2S(X̃ 1A1) and H2S+(X̃ 2B1,à 2A1,B̃ 2B2) electronic states. The global PESs were determined by the multireference configuration interaction calculations with the Davidson correction and the interpolant moving least squares method combined with the Shepard interpolation. The obtained FCFs exhibit that the H2S+(X̃) state primarily populates the vibrational ground state since its equilibrium geometry is almost equal to that of H2S(X̃), while the bending mode (ν2) is strongly enhanced for the H2S+(Ã) state; the maximum in the population is around ν2=6–7. In the same manner, the bending progressions are expected to consist of the great part of the H2S+(ÖX̃) emission. A detailed comparison with the experimental study for this system is reported in the accompanying paper, Paper II.

A theoretical study of the 1B1(O 1s → π*)and 1A1(O 1s → 3s)excited states of formaldehyde

The O 1s excited states of formaldehyde have been investigated theoretically usingthe restricted open-shell Hartree–Fock method for electronic structure calculationsand a linear vibronic coupling model for studying excited state nuclear dynamics.The results are compared with vibrationally resolved experimental data,published previously. In its 1B1(O 1s → π∗)state the molecule is found to be unstable with respectto the out-of-plane bending mode ν4(b1). Thelatter is a manifestation of vibronic coupling between the 1B1(O 1s → π∗)state and the next excited state, 1A1(O 1s → 3s).The dynamical calculations taking into account this interactionare in good agreement with experiment, whereas a simple Poissonintensity distribution reproduces only the main features of the spectralenvelope of the 1B1(O 1s → π∗)resonance. For the 1A1(O 1s → 3s)state, the Poisson distribution gives poor agreement with experiment,whereas the vibronic coupling model yields a more satisfactory description.

Vibrational Spectra of CO2-Electron Donor−Acceptor Complexes from ab Initio

In this paper, we investigated the 1:1 EDA complexes of CO2 formed with alcohols, namely, methanol and ethanol (sp3 O-donating atom), and with acetone (sp2 O-donating atom) in light of ab initio calculations. The interaction energy and the geometry of the complexes have been evaluated with the Moller−Plesset perturbation theory at the second-order level (MP2) using Dunning's basis sets. The predicted structures are found to be rather similar compared with the calculations at the SCF/3-21G* level reported by Jamroz et al. (Jamroz, M. H.; Dobrowolski, J. C.; Bajdor, K.; Borowiak, M. A. J. Mol. Struct. 1995, 349, 9.). Nevertheless, the stabilization energies are found in our work to be 2 to 2.5 times lower including electron correlation. In addition, we have analyzed the vibrational spectra of these EDA complexes. In particular, we emphasized the splitting of the ν2 bending mode of CO2 and the νS(OH) stretching mode of alcohols or the antisymmetric νa(CCC) and symmetric νs(CO) stretching modes of acetone. Finally, the shift and the IR and Raman intensity variations under the complex formation are discussed and compared with infrared absorption and Raman experimental measurements.