Comparison and assessment of procedures for calculating the R(12) line strength of the ν1 + 2 ν2 + ν3 band of CO2

Recently, results for the CO(2) R(12) line strength parameter have been reported, which differ significantly and are inconsistent with respect to quoted uncertainties. We investigate to what extent this inconsistency might be caused by the chosen data analysis methods. To this end, we assess and compare a parametric fitting procedure and a non-parametric approach. We apply the methods to simulated and measured line spectra, and we specify the conditions required for the safe application of the two procedures. For our present data, the corresponding conditions are satisfied for both methods, and consistent results are obtained. However, the simulations reveal that the fitting procedure can show shortcomings when the uncertainty in the wavenumber is large.     

Study of the ν1, ν1 + ν3 and ν2 + ν3 infrared bands of ONCl

A type (ΔK_a = 0) rovibrational lines of the near-prolate asymmetric top ¹⁶O¹⁴N³⁵Cl have been assigned on high resolution Fourier transform spectra: 820 lines of the ν₁ band, centered around 1800 cm⁻¹, 435 lines of the ν₁ + ν₃ band, centered around 2131 cm⁻¹, and 257 lines of the ν₂ + ν₃ band, centered around 925 cm⁻¹. Least-squares calculations have been carried out over these lines, using the A reduced Watson's hamiltonian in I^r representation; r.m.s. standard deviations of 0.0016 cm⁻¹, 0.0016 cm⁻¹ and 0.006 cm⁻¹ have been respectively obtained, making it possible to measure molecular constants of the (001), (101) and (011) vibrational levels of ¹⁶O¹⁴N³⁵Cl.     

Study of the ν2 + ν3 infrared band of ONCl

Two hundred and sixty A type rovibrational lines of the ν₂ + ν₃ vibrational band of ¹⁶O¹⁴N³⁵Cl, around 925 cm⁻¹, have been assigned; a least-squares calculation with a r.m.s. deviation of 0.0006 cm⁻¹ has made it possible to measure several constants of the (011) vibrational level.     

Radiochemistry of organometallic compounds: Studies with implanted ions—II 59Fe+ ions in [CpFe(CO)2]2

Attempts to stimulate hot atom reactions by the use of implanted radioactive ions have been extended to ⁵⁹Fe⁺ bombardment of [CpFe(CO)₂]₂ and [CpFe(CO)₂]I targets. These show modest yields of the labelled target compounds and small yields of labelled FeCp₂ and Fe(CO)₅. These yields show an expected decrease with increasing ion dose, but no significant dependence on beam energy in the range 20–80 keV. The product yields are 6·0, 3·0, 0·4 and 0·8% respectively for [CpFe(CO)₂]₂ targets and 0·7, 8·7, 0·1 and 0·2% respectively for [CpFe(CO)₂]I targets.These yields are markedly smaller than those from the neutron-bombarded compounds, which is taken to indicate that the “pure” recoil cannot account for a substantial fraction of the yields following neutron capture. The predominant yield of the target compound in each case is construed to mean that the reaction occurs at or near the end of the trajectory, by a hot displacement. The present data cannot distinguish whether the displacement occurs within less than one or more than one normal vibrational period of the interstitial projectile atom.     

The ν2 bending vibrational structure of the X̃2Σ+ state of MgNC

We have generated MgNC in supersonic free jet expansions and observed the laser induced fluorescence (LIF) of the A?(2)Π-X?(2)Σ(+) transition. We measured the LIF dispersed spectra from the single vibronic levels of the A?(2)Π electronic state of MgNC, following excitation of each ν(2) bending vibronic band observed, i.e., the κ series of the (0,v(2)('),0)-(0,0,0), v(2)(') = 0, 1, 2, 4, and 6 vibronic bands. In the vibrational structure in the dispersed fluorescence spectra measured, the long progression of the ν(2) bending mode in the X?(2)Σ(+) state is identified, e.g., up to v(2)(')=14 in the (0,6,0)-(0,v(2)('),0) spectrum. This enables us to derive the potential curve of the ν(2) bending mode in the X?(2)Σ(+) state. We used two kinds of models to obtain the potential curve; (I) the customary formula expressed in the polynomial series of the (v(2)(')+(d(2)/2)) term and (II) the internal rotation model. The potential curve derived from model (I) indicates the convergence of the bending vibrational levels at about 800 cm(-1) from the vibrationless level of MgNC, which may correspond to the barrier height of the isomerization reaction, MgNC ? MgCN, in the X?(2)Σ(+) state. Model (II) gives a simple picture for the isomerization reaction pathway with a barrier height of about 630 cm(-1) from the vibrationless level of the more stable species, MgNC. This shows that the v(2)(')=8 bending vibrational level of MgNC is already contaminated by the v(2)(')=2 bending vibrational level of the isomer, MgCN, and implies that the isomerization reaction begins at the v(2) (')=8 level. The bending potential surface and the isomerization reaction pathway, MgNC ? MgCN, in the X?(2)Σ(+) state are discussed by comparing the potential derived in this study with the surface obtained by quantum chemical calculation.     

Vibrational spectra and force constants of symmetric tops—XXII. Rotational analysis of ν2 + ν3 and ν1 + ν2 + ν3 of CF379Br and CF381Br

The rovibrational spectra of CF₃⁷⁹Br and CF₃⁸¹Br in the region of ν₂+ν₃ near 1120 cm⁻¹ and ν₁+ν₂+ν₃ near 2200 cm⁻¹ have been investigated with a resolution of 0.04 and 0.03 cm⁻¹ respectively. The rotational J structures have been resolved and were analyzed by means of polynomial and band contour simulation procedures. Molecular parameters (ν₀, x_ij, α^A,B) have been obtained from the analysis of the cold bands and the hot bands involving ν₆, 2ν₆, ν₃ and ν₅ for both isotopomers.     

Vibration—rotation spectrum of methyl cyanide— analyses of ν2 and ν3 + ν4 bands

Infrared spectrum of methyl cyanide was recorded in the region from 2235–2320 cm⁻¹ with a working resolution of 0.05 cm⁻¹. The transitions of two parallel type bands ν₂ and ν₃ + ν₄ as well as the associated hot bands are assigned. Since the molecular constants for the ground and ν₈ vibrational states are known precisely by microwave study for this molecule, highly accurate molecular constants for the upper vibrational states have been determined from those data by a least-squares procedure.     

Rovibrational study of the ν2 + ν±14, ν2 + 3ν±16, ν1 + ν±15, ν±14 + ν±15, ν±14 + ν±5, ν±5 + 3ν±16, ν±5 + 3ν±36 and ν1 + ν2 infrared bands of CH335Cl studied in a high-resolution FTIR spectrum from 4250 to 4600 cm−1

About 6400 lines belonging to the ν₂ + ν^±1₄, ν₂ + 3ν^±1₆, ν₁ + ν^±1₅, ν^±1₄ + ν^±1₅, ν^±1₄ + ν^±₅, ν^±₅ + 3ν^±1₆ and ν^±₅ + 3ν^±3₆ bands have been assigned. An r.m.s. deviation of 0.047 cm⁻¹ has been achieved by a least-squares fit of 1427 lines. For this purpose, a simplified model, taking into account five anharmonic resonances already found in a previous work [Molec. Phys. 70, 849 (1990)] and the well known x-y Coriolis resonance between the ν₂ and ν₅ modes of methyl halides, was used. Although not observed, the ν^±1₄ + ν^±1₅ and ν₁+ ν₂ parallel bands are strongly coupled by Coriolis resonance to ν₂ + ν^±1₄ and ν^±1₅ respectively. A few secondary resonances remain unexplained in several parts of the spectrum.     

State-to-state quantum dynamics of the N(4S) + OH(X2Π) → H(2S) + NO(X 2Π) reaction

Quantum state-to-state dynamics for the N((4)S) + OH(X(?2)Π) → H((2)S) + NO(X(?2)Π) reaction is reported on an accurate ab initio potential energy surface of the lowest triplet electronic state (a(3)A(")) of HNO∕HON. It was found that the reaction is dominated by long-lived resonances supported by the HNO and HON wells. Significant non-reactive scattering was observed, indicating substantial deviations from the statistical limit. Due to the large exothermicity of the reaction, the NO product has hot internal state distributions: its rotational state distribution is inverted and peaks near the highest accessible rotational level; and its vibrational state distribution extends to υ = 10 and decays monotonically with the vibrational quantum number. In particular, the predicted product vibrational distribution is in reasonably good agreement with experiment. The calculated differential cross section is dominated by scattering in both the forward and backward directions, consistent with the formation of reaction intermediates.     

Infrared diode laser spectroscopy of the ν2(2+ ← 1−) band of H3O+

Rotational lines in the ν₂ = 2⁺ ← 1⁻ “hot” band of the inversion mode of the oxonium (H₃O⁺) ion have been recorded by diode laser absorption spectroscopy. The ion was generated in low pressure gas discharges and detected using both velocity modulation and modulated hollow cathode techniques. Analysis of the spectra using a simple oblate symmetric top model has allowed the rotational parameters describing the 2⁺ inversion state to be determined for the first time. The band origin lies at 521.4383(52) cm⁻¹. These data will be useful in refining the oxonium ion inversion potential function and should aid in the analysis of other bands involving or perturbed by the 2⁺ level.     

FTIR spectra of the 2ν4, ν4 + ν6 and 2ν6 bands of formaldehyde

High resolution IR spectra of the overtones and the combination band of the ν₄ and ν₆ modes of formaldehyde (2ν₄, ν₄ + ν₆ and 2ν₆) were measured in the region of 2200–2650 cm⁻¹ using FTIR. The combination band ν₄ + ν₆, whose dipole transition is forbidden from molecular symmetry, was observed due to the intensity borrowed from the other bands. The observed frequencies were analysed by a Hamiltonian in which A-type Coriolis interactions and Darling—Dennison interaction were taken into account. The ratio and the relative signs of the transition dipole moments of the overtone bands, μ_2ν4 and μ_2ν6, have been determined by analysing the intensity distribution of the vibration—rotation lines.     

Quantum chemical study of chlorine-dissociation of oxalyl chloride (ClCO)_2→2Cl+2CO

It is very difficult to study the phenomenon that molecules are decomposed into several pho-tofragments by UV light, as the energy of lamp-house is insufficient. But the bond energy in oxa-lyl chloride is relatively low, for example, D0(ClCOCO-Cl) = 313.92 kJ/mol[1], D0(ClCO-CO) = 35.53 kJ/mol, and D0(Cl-CO) = 27.17 kJ/mol[2], so, oxalyl chloride, as a typical system for the study of multi-channel dissociation, can be dissociated into the four fragments Cl+Cl+CO+CO by the proper UV …     

Steric effect in the energy transfer reaction of oriented CO (a 3Π, v'=0, Ω=1 and 2) + NO (X 2Π) → NO (A 2Σ+, B 2Π) + CO (X 1Σ+)

The oriented CO (a (3)Π, v' = 0, Ω = 1 and 2) beam has been prepared by using an electric hexapole and applied to the energy transfer reaction of CO (a (3)Π, v' = 0, Ω = 1 and 2) + NO (X (2)Π) → NO (A (2)Σ(+), B (2)Π) + CO (X (1)Σ(+)). The emission spectra of NO (A (2)Σ(+), B(2)Π) have been measured at three orientation configurations (C-end, O-end, random). The shape of the emission spectra (and/or the internal excitation of products) turns out to be insensitive to the molecular orientation. The vibrational distributions of NO (A (2)Σ(+), v' = 0-2) and NO (B (2)Π, v' = 0-2) are determined to be N(v'=0):N(v'=1):N(v'=2) = 1:0.40 ± 0.05:0.10 ± 0.05 and N(v'=0):N(v'=1):N(v'= 2) = 1:0.6 ± 0.1:0.7 ± 0.1, respectively, and the branching ratio γ/β [=NO (A (2)Σ(+))/NO (B (2)Π)] is estimated to be γ/β ～ 0.3 ± 0.1 by means of spectral simulation. These vibrational distributions of NO (A, B) can be essentially attributed to the product-pair correlations between CO (X, v″) and NO (A (2)Σ(+), v' = 0-2), NO (B (2)Π, v' = 0-2) due to energetic restriction under the vibrational distribution of CO (X, v″) produced from the vertical transition of CO (a (3)Π, v' = 0) → CO (X, v″) in the course of energy transfer. The steric opacity function has been determined at two wavelength regions: 220 < λ < 290 nm [NO (A → X) is dominant]; 320 < λ < 400 nm [NO (B → X) is dominant]. For both channels NO (A (2)Σ(+), B(2)Π), a significant CO (a (3)Π) alignment effect is recognized; the largest reactivity at the sideways direction with the small reactivity at the molecular axis direction is observed. These CO (a (3)Π) alignment effects can be essentially attributed to the steric asymmetry on two sets of molecular orbital overlap, [CO (2π) + NO (6σ (2π))] and [CO (5σ) + NO (1π (2π))]. All experimental observations support the electron exchange mechanism that is operative through the formation of a weakly bound complex OCNO.     

Complex formation of HCONH2 in CH3OH environment and investigation of linewidth changes of ν(CO) stretching and NH2 bending modes

The isotropic part of the Raman bands corresponding to NH₂ bending and ν(CO) stretching modes of formamide (HCONH₂) at ∼1593 and 1668 cm⁻¹, respectively, in neat HCONH₂ as well as in binary mixtures with methanol (CH₃OH) were reinvestigated. Variations of their linewidths exclusively with mole fractions of HCONH₂, in the range C = 0.1–0.9 were studied. The linewidth variation of the NH₂ bending mode shows a departure from the trend expected on the basis of concentration fluctuation model and this has been explained using a recently suggested empirical model by invoking the concept of microviscosities of the solute, HCONH₂ and the solvent, CH₃OH. The other peak at ∼1668 cm⁻¹ shows a peculiar variation of the linewidth with concentration having two minima at C = 0.8 and 0.4, which have been explained in terms of formation of hydrogen bonded complexes, NH₂HCO⋯HOCH₃, and NH₂HCO⋯(HOCH₃)₂ and the two phenomena, namely motional narrowing and diffusion dynamics being simultaneously operative. The equilibrium constants have been evaluated from the spectral data and their variation with total molar concentration has been presented.     

Synthesis and reactions of ν2-(2-formylphenyl)tetracarbonylmanganese(I) complexes; cyclopentaanulation of a diterpenoid

Reaction of tetracarbonylmangenese(I) complexes derived from a diterpenoid aryl aldehyde or aryl methyl ketone with acetylene or ethylene leads to cyclopentaannulation to give 1H-inden-1-ols or 1H-indan-ols, respectively.     

Franck-Condon factors and radiative lifetime of the A2Π(1/2)-X2Σ+ transition of ytterbium monofluoride, YbF

The fluorescence spectrum resulting from laser excitation of the A(2)Π(1/2)←X(2)Σ(+) (0,0) band of ytterbium monofluoride, YbF, has been recorded and analyzed to determine the Franck-Condon factors. The measured values are compared with those predicted from Rydberg-Klein-Rees (RKR) potential energy curves. From the fluorescence decay curve the radiative lifetime of the A(2)Π(1/2) state is measured to be 28 ± 2 ns, and the corresponding transition dipole moment is 4.39 ± 0.16 D. The implications for laser cooling YbF are discussed.     

Vibrational spectra and force constants of symmetric tops—XLII. Rovibrational spectra of CF3I in the ν2, ν3, 2ν3 and ν2 + ν3 regions

The gas phase i.r. spectrum of CF₃I has been investigated in the ν₂, ν₃, 2ν₃ and ν₂ + ν₃ region with a resolution of 0.04 cm⁻¹. Rotational J clusters have been resolved, and several vibrational and rovibrational parameters of ν₂, 743.364(8) cm⁻¹ and ν₃, 286.303(3) cm⁻¹, have been determined by polynomial methods and by band contour simulation.     

Temperature dependence of the ν(OH) bands of hydroxyapatites

The effect of temperature upon the ν(OH) bands of nine hydroxy apatites has been studied and discussed in relation to earlier results.     

Chemical dynamics of the CH(X2Π) + C2H4(X1A1g), CH(X2Π) + C2D4(X1A1g), and CD(X2Π) + C2H4(X1A1g) reactions studied under single collision conditions

The crossed beam reactions of the methylidyne radical with ethylene (CH(X(2)Π) + C(2)H(4)(X(1)A(1g))), methylidyne with D4-ethylene (CH(X(2)Π) + C(2)D(4)(X(1)A(1g))), and D1-methylidyne with ethylene (CD(X(2)Π) + C(2)H(4)(X(1)A(1g))) were conducted at nominal collision energies of 17-18 kJ mol(-1) to untangle the chemical dynamics involved in the formation of distinct C(3)H(4) isomers methylacetylene (CH(3)CCH), allene (H(2)CCCH(2)), and cyclopropene (c-C(3)H(4)) via C(3)H(5) intermediates. By tracing the atomic hydrogen and deuterium loss pathways, our experimental data suggest indirect scattering dynamics and an initial addition of the (D1)-methylidyne radical to the carbon-carbon double bond of the (D4)-ethylene reactant forming a cyclopropyl radical intermediate (c-C(3)H(5)/c-C(3)D(4)H/c-C(3)H(4)D). The latter was found to ring-open to the allyl radical (H(2)CCHCH(2)/D(2)CCHCD(2)/H(2)CCDCH(2)). This intermediate was found to be long lived with life times of at least five times its rotational period and decomposed via atomic hydrogen/deuterium loss from the central carbon atom (C2) to form allene via a rather loose exit transition state in an overall strongly exoergic reaction. Based on the experiments with partially deuterated reactants, no compelling evidence could be provided to support the formation of the cyclopropene and methylacetylene isomers under single collision conditions. Likewise, hydrogen/deuterium shifts in the allyl radical intermediates or an initial insertion of the (D1)-methylidyne radical into the carbon-hydrogen/deuterium bond of the (D4)-ethylene reactant were found to be-if at all-of minor importance. Our experiments propose that in hydrocarbon-rich atmospheres of planets and their moons such as Saturn's satellite Titan, the reaction of methylidyne radicals should lead predominantly to the hitherto elusive allene molecule in these reducing environments.