Vibration-rotation analysis of the jet-cooled v12, v7 + v8 and v6 + v10 absorption bands of 12C2H4

A Fourier transform interferometer was used to record the slit-jet cooled absorption spectrum of ¹²C₂H₄ between 700 and 2400 cm^?1I, at a spectral resolution of 0.005 cm^?1. Three bands, v₁₂ at 1442.442 70(1)cm^?1, v₇ + v₈ at 1888.978 23(3)cm^?1 and v₆ + v₁₀ at 2047.775832(2)cm^?1, were rotationally analysed. In the case of 7¹8¹, a known Coriolis perturbation mechanism involving the nearby 4¹8¹ (1958.264cm^?1) and 8¹10¹ (1766.391 cm^?1) states was accounted for in the analysis. The latter fitting procedure included 12 levels from the 4¹8¹ state which are observed because lines from v₄ + v₈ borrow intensity from v₇ + v₈. Compared to the literature, significantly improved vibration-rotation constants were obtained for all upper states reported in the present study.     

The infrared spectrum of C3O2: The interaction between ν7 and the ν2 and ν4 vibrations

The 3ν¹₇, 3ν³₇, and 4ν⁰₇ hot bands of the ν₄ fundamental of C₃O₂ in the 1580 cm^?1 region were analyzed from tunable diode laser spectra and the ground state to ν₄ + 2ν⁰₇ band at 1644 cm^?1 from Fourier transform spectra (FTS). The molecular constants for all of the v₄ 1 ← 0 bands as well as the intensity of the ν₀ + 2ν⁰₇ sum band relative to the ν₄ fundamental were in agreement with the predictions of the model of Weber and Ford. FTS spectra at 0.05 cm^?1 resolution were obtained of the sum and difference bands of ν₂ with ν₇ in the 750–900 cm^?1 region. Sharp Q branches occur for each ν₇ state in the sum bands, but only a number of R-branch bandheads and no recognizable Q branches in the difference bands. Assignments of the sum band Q branches through v₇ = 6 were made and molecular constants were determined for the ν₂ + ν¹₇ ← 0 transition at 819.7 cm^?1. The ν₇ potential function in the v₂ = 1 state was found to have a 1.2 cm^?1 barrier with a minimum at α = 4.9°, where 2α is the angular deviation from linearity. The Q-branch positions predicted from the calculated energy levels fit those observed within several cm^?1.     

Formation and quenching mechanisms of excited particles in an oxygen-iodine laser medium

New values of a number of kinetic constants of processes proceeding in oxygen-iodine laser media are presented. The total probabilities of formation of I₂(X, 15 ≤ v ≤ 24) and I₂(X, 25 ≤ v ≤ 47) molecules in the course of quenching of I* atoms by I₂(X) are found to be 0.9 and 0.1, respectively. The quantum yield of singlet oxygen in the reaction O(¹ D) + N₂O → N₂ + O₂(a ¹Δ) is close to 100%. The quenching rate constants of I₂(A’) by O₂, H₂O, CO₂, I₂, and Ar and of I(² P _1/2) by O(³ P), O₃, NO₂, N₂O₄, and N₂O are presented.     

Acetylene, 12C2H2: new CRDS data and global vibration-rotation analysis up to 8600 cm−1

The absorption spectrum of ¹²C₂H₂ has been recorded using cavity ringdown spectroscopy and analyzed in the ranges 6000 ? 6356 cm^?1 and 6667?7015 cm^?1. Fourteen new bands have been identified and additional J-lines were assigned in 10 already known bands. These new data, together with the published vibration–rotation absorption lines of ¹²C₂H₂ accessing vibrational states up to 8600 cm^?1 have been gathered in a database. The resulting set includes 12137 transitions involving 186 different k = l ₄ + l ₅ sub-states, with l _i the angular momentum quantum number associated to the i degenerate bending vibration. These lines have been fitted simultaneously to spectroscopic parameters through J-dependent Hamiltonian matrices exploiting the vibrational polyad or cluster block-diagonalization, in terms of the pseudo-quantum numbers N_r = 5v ₁ + 3v ₂ + 5v ₃ +v ₄ +v ₅ and N_s = v ₁ + v ₂ + v ₃, also accounting for k and e/f parities and u/g symmetry. Modes 1 and 2 correspond to the symmetric CH and CC stretchings, mode 3 to the antisymmetric CH stretch, and modes 4 and 5 to the trans- and cis-degenerate bendings, respectively. The fit was successfully achieved, with a dimensionless standard deviation of 0.92, leading to the determination of 266 effective vibration-rotation parameters.     

Infrared radiation properties of methane at elevated temperatures

The spectral absorptivity of the v₃ and v₄ fundamental and the v₁ + v₄ combination bands of methane have been measured at low resolution for temperatures between 290 and 850 K. Spectral mean (narrow-band) parameters for the fundamental bands have been correlated from the Elsasser model, while total band absorptance data for all three bands have been correlated using the Edwards exponential wide band model. A total emissivity chart has been developed, based on the wide band absorption models.     

Distribution of cations in magnetite prepared by mechanochemical synthesis

The distribution of iron cations in the crystal lattice of the Fe_3?vO₄ (v=0.153) cation-deficient spinel produced by mechanical dispersion of α-Fe₂O₃ hematite in water is investigated using x-ray diffraction and Mössbauer spectroscopy. Analysis of the Mössbauer data shows that the Fe_2.847O₄ magnetite prepared by mechanochemical synthesis is a chemically heterogeneous compound. The crystal structure of Fe_2.847O₄ is characterized by local environments of the (Fe^2.5+)₀ cations at v₀≤0.1, v₁?0.12, v₂?0.18, and v₃?0.26, which are responsible for a broad distribution of magnetic hyperfine fields with the P(H) probability maxima near 37.0, 36.0, 34.0, and 30.0 MA m^?1.     

Line strengths,spin-splittings,and forbidden transitions in the (101) band of 14N16O2

Measurements of line strengths in the (101) and (111)-(010) bands of ¹⁴N¹⁶O₂ have been made at a resolution of 0.02 cm^?1 in the region 2863 to 2934 cm^?1. The strength data in the (101) band were analyzed to determine a vibrational band strength and coefficients of the F factor. Each subband for K_?1 ≤ 9 was analyzed separately and all the F-factor coefficients in terms of the rotational quantum number, N, were found to be too small to be of significance. However, F was found to be dependent on K_?1 and the experimentally determined subband strengths were least-squares fitted to the expression S_v⁰·F, where S_v⁰ = 68.3 cm^?2 atm^?1 at 296 K and F = 1 + (2.899 × 10^?3)K_?1 + (4.08 × 10^?3)K_?1² ? (2.34 × 10^?4)K_?1³. The integrated strengths for the (101) and (111)-(010) bands were found to be 70.9 ± 2.3 and 2.7 ± 0.3 cm^?2 atm^?1 at 296 K, respectively. Also included in this study are measurements of line center positions in the two bands and spin-splittings in the (101) band. Recent frequency measurements of lines with K_?1 ≤ 8 in the (101) band have been made at a resolution of 0.0033 cm^?1 by V. Dana and J. P. Maillard (J. Mol. Spectrosc.71, 1–4) (1978)) for the region above 2889 cm^?1 and our values are in excellent agreement with theirs. Separations of the split lines measured in this work (K_?1 ≤ 10) agree well with calculated values using expressions which include the η_aaaaK_?1⁴ term with η′_aaaa = ?1.70 ± 0.15 × 10^?4 cm^?1 as derived for the (101) state. Three forbidden (ΔN ≠ ΔJ, ΔK_?1 = 0) transitions in the (101) band were observed with their identifications based on the agreement between measured and calculated line positions and strengths.     

Predissociation linewidths and oscillator strengths for the (2-0) to (13-0) Schumann-Runge bands of O2

Analysis of the absorption spectrum of O₂ in the Schumann-Runge bands (B³Σ_u^?-X³Σ_g^?) from the 2-0 to the 13-0 band yields oscillator strengths which are in good agreement with past theoretical calculations. Predissociation linewidths deduced from the data tend to be larger than theoretical predictions for v′ ≤ 5 and are reasonably near theory for v′ > 5. The qualitative dependence of the linewidths on vibrational level is in accord with that expected for a repulsive potential intersecting the B³Σ state near v′ = 4. For a given band the predissociation linewidth deduced from the spectra tends to increase as the total angular momentum increases. The new linewidths are smaller than some past experimental results, and this will have an impact on future calculations of the photodissociation rates of O₂, NO, and H₂O in the earth's upper atmosphere.     

Solvatochromic properties of long alkyl chain π* indicators: comparison of N,N‐dialkyl‐4‐nitroanilines and alkyl 4‐nitrophenyl ethers

Hydrophobic forms of the N,N‐dialkyl‐4‐nitroaniline (DNAP) (p‐O₂NC₆H₄NR₂) ( 1a–f ) and alkyl‐4‐nitrophenyl ether (p‐O₂NC₆H₄OR) ( 2a–c ) solvatochromic π* indicators have been characterized and compared with respect to: (a) solvatochromic bandshape, (b) sensitivity expressed as ?s , ( / d π * ), and (c) trends in ? s with increasing length of alkyl chain(s) on the probe molecule. ? Octyl 4‐nitrophenyl ether (p‐O₂NC₆H₄OC₈H₁₇) ( 2b ) and ? decyl 4‐nitrophenyl ether (p‐O₂N C₆H₄ OC₁₀H₂₁) ( 2c ) were synthesized and their solvatochromic UV/Vis absorption bands were found to maintain a Gausso‐Lorentzian bandshape for the indicators in non‐polar and alkyl substituted aromatic solvents, for example, hexane(s) and mesitylene. Corresponding absorption bands for 1a–f display increasing deviation from a Gausso‐Lorentzian shape in the same solvents as the alkyl chains on the indicator are increased in length all the way to C₁₀ and C₁₂, for example, N,N‐didecyl‐4‐nitroaniline (p‐O₂NC₆H₄N (C₁₀H₂₁)₂) and N,N‐didodecyl‐4‐nitroaniline (p‐O₂NC₆H₄N (C₁₂H₂₅)₂) ( 1d–f ). A plot of ? s versus C_n follows a 1st order decay for the DNAP indicators but is linear for the alkyl 4‐nitrophenyl ethers. A discussion of how the long alkyl chains on the two types of indicators affect the orientation and overlap of n and π * orbitals, and resulting solvatochromic bands is presented. For DNAP, overextending the alkyl chains to obtain greater hydrophobic character may cause the alkane component to dominate solute‐solvation processes at the expense of the probe's fundamental solvatochromic character. Copyright © 2007 John Wiley & Sons, Ltd.     

Optical properties of crystals doped with Sm3+ or Dy3+ relevant to potential InGaN/GaN laser diode-pumped visible laser operation: A comparative study

Results of detailed spectroscopic investigation of Sm³⁺ and Dy³⁺ ions incorporated in crystal structures of Yal YAl₃(BO₃)₄, LiNbO₃, Gd₃Ga₅O₁₂, Gd₂SiO₅, Lu₂SiO₅ and (Gd, Lu)₂SiO₅ are reported and discussed. The impact of the hosts on transition intensities and excited state relaxation dynamics of incorporated luminescent ions was examined. Distribution of luminescence intensity among spectral bands in terms of luminescence branching ratios was evaluated based on numerical integration of luminescence bands. Intensities of UV and blue absorption bands potentially useful for optical pumping were determined quantitatively in units of absorption cross section. The most intense luminescence bands related to potential laser transitions ⁴ G _5/2 → ⁶ H _7/2 of Sm³⁺ around 600 nm and ⁴ F _9/2 → ⁶ H _13/2 of Dy³⁺ around 580 nm were calibrated in units of emission cross section. Evaluated peak values of emission cross section range from 0.43 × 10^?20 cm² for Sm³⁺ in (Gd, Lu)₂SiO₅ to 1.17 × 10^?20 cm² for Sm³⁺ in LiNbO₃. Those for dysprosium-doped crystals range from 0.63 × 10^?20 cm² for LiNbO₃:Dy³⁺ to 2.0 × 10^?20 cm² for Yal YAl₃(BO₃)₄:Dy³⁺. It follows from these considerations that samarium-doped crystals show promise for laser application owing to the combination of a strong absorption that matches radiation of commercial laser diodes emitting near 405 nm and long luminescence lifetime. Major shortcoming of dysprosium-doped crystals results from a weak intensity of absorption bands available for optical pumping near 450 nm and 385 nm combined with relatively strong self-quenching of luminescence.     

Investigation of the kinetics of OH∗ and CH∗ chemiluminescence in hydrocarbon oxidation behind reflected shock waves

The temporal variation of chemiluminescence emission from OH^?(A² Σ ⁺) and CH^?(A² Δ) in reacting Ar-diluted H₂/O₂/CH₄, C₂H₂/O₂ and C₂H₂/N₂O mixtures was studied in a shock tube for a wide temperature range at atmospheric pressures and various equivalence ratios. Time-resolved emission measurements were used to evaluate the relative importance of different reaction pathways. The main formation channel for OH^? in hydrocarbon combustion was studied with CH₄ as benchmark fuel. Three reaction pathways leading to CH^? were studied with C₂H₂ as fuel. Based on well-validated ground-state chemistry models from literature, sub-mechanisms for OH^? and CH^? were developed. For the main OH^?-forming reaction CH+O₂=OH^?+CO, a rate coefficient of k ₂=(8.0±2.6)×10¹⁰ cm³?mol^?1?s^?1 was determined. For CH^? formation, best agreement was achieved when incorporating reactions C₂+OH=CH^?+CO (k ₅=2.0×10¹⁴ cm³?mol^?1?s^?1) and C₂H+O=CH^?+CO (k ₆=3.6×10¹²exp(?10.9 kJ?mol^?1/RT) cm³?mol^?1?s^?1) and neglecting the C₂H+O₂=CH^?+CO₂ reaction.     

Electronic-excitation transfer collisions in flames—V. Cross sections for quenching and doublet-mixing of K(42P)-doublet by N2, O2, H2 and H2O

Weighted average cross sections for quenching of the K(4²P)-doublet by N₂, H₂, O₂ and H₂O, measured in flames, show no significant temperature dependence in the range from 1500 to 2500K. Doublet mixing cross sections for K(4²P$\text{3}\text{2}$?4²P$\text{1}\text{2}$) transitions were measured at 1720K for N₂, O₂, H₂O. The ratios of both mixing cross sections were measured independently and were found to agree with the detailed balance condition within 2 per cent. It is shown that an ionic intermediate-state model cannot explain the large magnitude of N_2? mixing cross sections.     

The high resolution infrared spectrum of the 2ν2 + ν3 and ν1 + ν2 + ν3 bands of 14N16O2: Vibration and vibration-rotation constants of the electronic ground state of 14N16O2

The A-type bands, 2ν₂ + ν₃ and ν₁ + ν₂ + ν₃, with band centers at 3092 and 3638 cm^?1, respectively, of ¹⁴N¹⁶O₂ have been measured with resolution of 0.03 cm^?1 or better. Spectroscopic constants have been derived for the upper states of both bands. Infrared determined band constants have been combined with laser-excited resonance fluorescence data to obtain a set of vibration and vibration-rotation constants for the ground state of ¹⁴N¹⁶O₂.     

l-Resonance effects in the hot bands 3v 5 ← 2v 5, (v 4 + 2v 5) ← (v 4 + v 5) and (2v 4 + v 5) ← 2v 4 of acetylene

In the infrared spectrum of C₂H₂ around the fundamental v ₅, the hot bands starting from the levels 2v ₅, 2v ₄ and v ₄ + v ₅ have been investigated. From the analysis of about 20 different bands, 40 molecular constants describing the bending modes v ₄ and v ₅ have been derived.     

Thermal depolarization in crystals of calcium fluoride doped with oxygen

The study of thermally induced depolarization (TD) in crystals of calcium fluoride doped with oxygen reveals the existence of nearest-neighbour (nn) dipolar complexes comprising substitutional oxide ions (O_s^2?) and fluoride ion vacancies (F_v^?) on nn sites. Evidence for this relaxation is seen in TD experiments both on pure calcium fluoride doped with oxygen and on Na⁺ doped CaF₂ crystals that had been heated in air. Similar measurements on CaF₂: Y³⁺, O^2? reveal six separate relaxations, two of which are due to Y_s^3??F_i^? complexes that do not involve oxygen, one is due to O_s^2??F_v^? dipoles, and one is t the T₁ complex, Y_s³⁺ (O^2?)₄(F_v^?)₃. The remaining two relaxations were not identified but are probably d larger defect clusters.     

Absolute line wavenumbers in the near infrared: 12C2H2 and 12C16O2

40 absolute line wavenumbers in the 3v ₃ band of ¹²C¹⁶O₂ between 6927 cm^?1 and 6989 cm^?1 and 626 absolute line wavenumbers in the near infrared absorption spectrum of ¹²C₂H₂ between 7060 cm^?1 and 9900 cm^?1 have been measured using high resolution Fourier transform spectroscopy. The calibration of the CO₂ line wavenumbers relied on heterodyne frequencies available in the v ₁ + v ₃ band of ¹²C₂H₂ near 6556 cm^?1. The absolute uncertainty of the calibrated CO₂ line wavenumbers is estimated to 0.000 08 cm^?1. The acetylene spectra were calibrated using heterodyne frequencies available in the 2—0 band of ¹²C¹⁶O and the line wavenumbers obtained in the 3v ₃ band of ¹²C¹⁶O₂. The absolute uncertainty of the calibrated acetylene line wavenumbers is estimated to range from 0.0003 cm^?1 to 0.006 cm^?1 for strong to very weak isolated lines. Comparison with absolute line wavenumbers obtained independently at JPL in the 3v ₃ band of ¹²C₂H₂ near 9649 cm^?1, calibrated using absolute wavenumbers available in the 2—0 and 3—0 (near 6350 cm^?1) bands of ¹²C¹⁶O, shows very good agreement. Also, the vibration—rotation constants for the observed upper vibrational states of ¹²C₂H₂ were determined, but without accounting for the perturbations affecting these states.     

12C16O2: Σ and Π Fermi dyads in the 4.5-μm region: Wavenumbers and spectroscopic constants

Emission spectra of CO₂ vibrationally excited by a dc electric discharge were recorded under Doppler-limited resolution, using the high information interferometer of Laboratoire d'Infrarouge Orsay, France, in the spectral region 4–5 μm. Sixteen bands with Δv₃ = 1 of ¹²C¹⁶O₂ involving the Fermi dyads (10⁰v₃, 02⁰v₃)_{I and II} and (11¹v₃, 03¹v₃)_{I and II} have been studied. The band centers and the spectroscopic constants for all the vibrational levels involved are given. They reproduce the experimental wavenumbers with a rms of the order of 4 × 10^?5 cm^?1 for the best vibrational transition and always less than 3 × 10^?4 cm^?1 for the others. These results are compared with laser measurements for the (10⁰0, 02⁰0) dyad.     

Adsorption of small molecules on transition metal doped rhodium clusters Rh3X (X = 3d, 4d atom): a first-principles investigation

The adsorption behaviours of seven molecules (CO, CO₂, N₂, NO, O₂, N₂O and NO₂) on Rh₃X (X?=Sc-Zn, Y-Cd) clusters are systematically investigated by density-functional calculations. Rh₃X clusters exhibit physical adsorption when interacting with CO₂, CO, N₂ and NO. The adsorption energies (E_ads) can be ranked as follows: NO?>?CO?>?CO_2?≥?N₂. Compared with pure Rh₄ cluster, the adsorption capacity changes with the doping element. Chemical adsorption can be obtained for Rh₃X when adsorbing O₂, N₂O and NO₂. E_ads shows an order of E_ads(O₂)?>?E_ads(NO₂)?>?E_ads(N₂O). When O₂ is adsorbed, energy barrier with doping Tc or Cr atom is substantially reduced, which indicates that chemical reactivity of O₂ on Rh₄ can be significantly enhanced. The doped rhodium clusters can be viewed as good candidates in the discrimination between different gas molecules.     

Charge-transfer bands in crystals of alkaline earth fluorides with Eu<Superscript>3+</Superscript> and Yb<Superscript>3 + 1</Superscript>

The absorption, luminescence, and excitation spectra of CaF₂, SrF₂, and BaF₂ crystals with EuF₃ or YbF₃ impurity have been investigated in the range 1–12 eV. In all cases, strong wide absorption bands (denoted as CT₁) were observed at energies below the 4f ⁿ -4f ^{n ? 1}5d absorption threshold of impurity ions. Weaker absorption bands (denoted as CT₂) with energies 1.5–2 eV lower than those of the CT₁ bands have been found in the spectra of CaF₂ and SrF₂ crystals with EuF₃ or YbF₃ impurities. The fine structure of the luminescence spectra of CaF₂ crystals with EuF₃ impurities has been investigated under excitation in the CT bands. Under excitation in the CT₁ band, several Eu centers were observed in the following luminescence spectra: C _4v , O _h , and R aggregates. Excitation in the CT₂ bands revealed luminescence of only C _4v defects.