Dynamics of CO2 molecules confined in the micropores of solids as studied by C NMR

The pressure and temperature dependence of ¹³C NMR of CO₂ adsorbed in several porous materials was measured. For CO₂ in activated carbon fiber (ACF), the spectrum observed in the pressure range from 0 to 10 MPa consisted of two lines. A very sharp peak at δ = 126 ppm was attributed to free CO₂ gas and a broad peak at δ = 123 ppm was attributed to confined CO₂ molecules in the micropores of ACF, although CO₂ in microporous materials such as zeolites and mesoporous silica, gave only a single peak attributed to free CO₂ gas. In the low-pressure region, the peak at δ = 123 ppm shifted to 118 ppm and a very broad peak with a line width of about 200 ppm appeared. This indicates that there are two kinds of CO₂ molecules confined in ACF with different rates of molecular motion: one is undergoing isotropic rotation and the other is undergoing anisotropic motion, which rotates around an axis tilted by 30° from the molecular axis. This implies that small pockets with a characteristic diameter exist on the surface of the ACF micropore.     

High accurate peak positions for calibration purposes with the lowest fundamental bands ν2 of N2O and CO2

The lowest fundamental vibration rotation bands ν₂ of nitrous oxide (N₂O) and carbon dioxide (CO₂) have been measured with a Fourier transform spectrometer at the resolution of 0.001 cm⁻¹. The spectra have been calibrated with the high accurate peak positions of the carbonyl sulfide (OCS) ν₂ band, which has been recently produced as a candidate for a secondary standard by calibrating first the 2ν₂ band with the CO₂ laser bands around 10 μm and then transferring the calibration to ν₂ with the internal energy levels of OCS. In the present work the OCS ν₂ and ν₁ bands were measured together with the spectra of N₂O and CO₂. Then the OCS ν₁ band was measured by calibrating it with the 2ν₂ band of OCS. The linearity of the wavenumber scale was checked by comparing the corresponding line positions in the OCS ν₁ band in these two separate measurements. The absolute accuracy of the ν₂ band centers of N₂O and CO₂ were evaluated to be 6.8 × 10⁻⁶ and 8.4 × 10⁻⁶ cm⁻¹, respectively.     

Raman intensity measurements of the Fermi diad ν1, 2ν2 in CO2 and CO2

Intensity measurements of the ν₁, 2ν₂ vibrational Raman bands of ¹²CO₂ and ¹³CO₂ lend support to Amat's suggestion that the unperturbed 02⁰0 level is above the 10⁰0 level for ¹²CO₂. For ¹³CO₂, however, the ordering of the levels is reversed.     

N2- and O2-broadening of CO2 for the (301)III ← (000) band at 6231 cm

The N₂- and O₂-broadening effect have been investigated for 10 absorption lines of the CO₂ (30⁰1)_III ← (00⁰0) band centered at 6231 cm⁻¹, in the range from P(28) to R(28) by a near-infrared diode-laser spectrometer. We have analyzed the observed line profiles with the Galatry function, and determined the N₂- and O₂-broadening coefficients precisely. The air-broadening coefficients for these lines have been derived. The present results are compared with those of the previous studies for this band and with some of the other bands.     

CO2-broadened water in the pure rotation and ν2 fundamental regions

The CO₂-broadened water coefficients (half-widths, line shifts, and temperature dependence of the widths) are predicted using a fully complex Robert-Bonamy formulation for the 937 allowed and forbidden perpendicular type transitions of (000)-(000) between 200 and 900 cm⁻¹ in order to facilitate atmospheric remote sensing of Mars and Venus. In addition, empirical Lorentz line widths and pressure-induced frequency-shifts of CO₂-broadened H₂¹⁶O are obtained at room temperature for 257 perpendicular transitions of the (010)-(000) fundamental. For this, calibrated spectra recorded at 0.0054 cm⁻¹ resolution are measured assuming Voigt line shapes. For transitions between 1287 and 1988 cm⁻¹ with rotational quanta up to J = 13 and K_a = 6, the widths vary from 0.045 to 0.212 cm⁻¹ atm⁻¹ at 300 K; the pressure-shifts are quite large and range from −0.0386 to +0.0436 cm⁻¹ atm⁻¹. For the (010)-(000) band, the RMS and mean observed and calculated differences for CO₂-broadened H₂O half-widths are 12% and −1.9%, respectively, while the RMS and mean ratios of the observed and calculated pressure-induced shift coefficients are 1.6 and 0.79, respectively. For pairs of transitions involving K_a = 0 and 1, such as 2_0 2 ← 3_1 3 and 3_1 3 ← 2_0 2, both the calculated and observed pressure induced shifts in positions are opposite in sign and often similar in magnitude. The data are too limited to characterize vibrational dependencies of the widths, however.     

Absolute frequency measurement of CO2 laser lines with a femtosecond laser comb and new determination of the CO2 molecular constants and frequency grid

Absolute frequency measurements of a CO₂ laser stabilized on saturated absorption resonances of CO₂ laser lines are reported. They were performed using a femtosecond-laser frequency comb generator and two laser diodes at 852 and 782 nm as intermediate oscillators, with their frequency difference phase-locked to the CO₂ laser. Twenty ¹²C¹⁶O₂ laser lines in the P and R bands at 9 μm were measured with a relative uncertainty of a few 10⁻¹² limited by the CO₂ frequency reproducibility. A new determination of the CO₂ molecular constants was obtained from these data and previous measurements in the 10 μm band. The CO₂ frequency grid was also calculated, with an improvement of two orders of magnitude compared to the previous grid of Maki et al. [J. Mol. Spectrosc. 167 (1994) 211].     

Determination and analysis of dispersive optical constant of TiO2 and Ti2O3 thin films

Electron beam evaporation technique was used to prepare TiO₂ and Ti₂O₃ thin films onto glass substrates of thicknesses 50, 500 and 1000 nm for each sample. The structural investigations revealed that the as-deposited films are amorphous in nature. Transmittance measurements in the wavelength range (350-2000 nm) were used to calculate the refractive index n and the absorption index k using Swanepoel's method. The optical constants such as optical band gap , optical conductivity σ_opt, complex dielectric constant, relaxation time τ and dissipation factor tan δ were determined. The analysis of the optical absorption data revealed that the optical band gap E_g was indirect transitions. The optical dispersion parameters E_o and E_d were determined according to Wemple and Didomenico method.     

Study of the CO2 decomposition over doped Ni-ferrites

The H₂ reduced NiFe_2−xCr_xO₄ can be used to decompose CO₂ to C repeatedly. A series of nanocrystalline Ni-ferrite doping different contents of Cr³⁺ were synthesized by mixed ions co-precipitation method and characterized by XRD, BET and TEM. The results showed that their crystallite sizes were 1-2 nm and BET surface area changed from 220 to 285 m²/g. The evaluation of the activity and stability indicated that Ni-ferrite with 4 wt% Cr³⁺ dopant could be used repeatedly as many as 60 times and was transformed to Fe_yNi_1−y (0<y<1) alloy and Fe₅C₂ gradually during the cycle decomposition of CO₂ to carbon, especially for no Cr³⁺ sample. After the 60th reaction, although NiFe₂O₄ phase just remained 2.1 wt%, the decomposition activity of Ni-ferrite with 4 wt% Cr³⁺ was still 60% of initial activity. This fact suggests that nanocrystalline Fe_yNi_1−y (0<y<1) alloy from the cycle reaction can contribute to the decomposition of CO₂. The results from scanning electron microscopy (SEM), TEM and XRD show that the deposited carbon from CO₂ decomposition consisted of amorphous, crystallite and carbon nanotubes.     

Absorption spectra of CO2 and CO2 near 1.05 μm

The absolute line intensities of the Fermi triad 2003i-00001 (i = 1, 2, 3) of ¹²C¹⁶O₂ and ¹³C¹⁶O₂ isotopic species of carbon dioxide were retrieved from Fourier-transform spectra recorded at Doppler limited resolution in the region 9200-9700 cm⁻¹. The accuracy of the line intensity determination is estimated to be better than 15% for most lines. The vibrational transition dipole moments squared and Herman-Wallis coefficients have been determined. The global fittings of the observed line intensities within the framework of the effective operators method have been performed. The fitting results reproduce the data within experimental uncertainty.     

Collision induced absorption spectra of the fundamental band of D2 in binary mixtures D2-Kr at 298 K

The enhancement spectrum of the collision induced absorption of D₂ in its fundamental band region 2600-4000 cm⁻¹ in binary mixtures D₂-Kr was studied at 298 K for base densities of D₂ in the range 9-20 amagat and for partial densities of Kr in the range 7-120 amagat. The binary absorption coefficient of the band has been determined from the measured integrated absorption coefficient and found to be 3.9 × 10⁻³ cm⁻² amagat⁻². An analysis of the experimental spectrum was carried out by assuming appropriate line-shape functions and the half-width parameters δ₁, δ₂, δ_d and δ_c of the long range quadrupole, and of the short range overlap induced transitions have been determined. Good agreement was obtained between the recorded spectrum of the fundamental band and the synthetic profile.     

Infrared spectrum of the continuum and dimer absorption in the vicinity of the O2 vibrational fundamental in O2/CO2 mixtures

The intensities of the collision-induced absorption (CIA) bands associated with the electric-dipole forbidden O₂ fundamental and the CO₂ν₁/2ν₂ Fermi dyad monomer vibrational bands have been studied over the temperature range 193-360 K and the frequency range 1100-2000 cm⁻¹. As CO₂ is added to a pure O₂ sample, the intensity in the O₂ fundamental band region increases dramatically. At the lowest temperature studied, 193 K, the band-integrated CIA coefficient for enhancement of the Fermi dyad absorption from CO₂ to CO₂ collisions, S_CO2-CO2, is more than a factor of two larger than the band-integrated CIA coefficient for enhancement of the O₂ vibrational fundamental by CO₂ collisions, S_O2-CO2. Moreover, the S_CO2-CO2 coefficient shows a significantly larger temperature dependence, increasing by more than a factor of two from 345.6 to 193 K while S_O2-CO2 increases by less than one third. The band shapes and their temperature dependence provide clear evidence for the formation of CO₂-CO₂ and CO₂-O₂ complexes. The CO₂-CO₂ dimer feature is most striking, contributing significantly to the infrared absorption near the expected CO₂ monomer fundamentals. Evidence for the more weakly bound CO₂-O₂ complex is seen on the O₂ CIA band, particularly at the lowest temperatures studied. The shapes for both dimer bands display sharp a-type Q branch central profiles and broad P and R branch like structure attributed to b-type Q branches for the CO₂-CO₂ complex and a-type P and R branch structure for the CO₂-O₂ complex. The present results stress the importance of including bound and metastable dimer absorption in any theoretical modeling of CIA, particularly when one of the collision partners has a large electrostatic moment, such as CO₂ with its large electric quadrupole moment.     

Linewidths of HCl broadened by CO2 and N2 and CO broadened by CO2

High resolution measurement of the linewidths of HCl broadened by CO₂ and N₂ and CO broadened by CO₂ have been performed in both the 1-0 and 2-0 bands of HCl and the 2-0 band of CO. The data were analyzed by the direct and the peak absorption methods. Values of the linewidths obtained by the two methods are in good agreement. For |m| ≤ 3, for the case of HCl + CO₂, the agreement is good for the values obtained in both bands of HCl. However for |m| > 3, the HCl + CO₂ linewidths in the 1-0 band are smaller than the corresponding lines in the 2-0 band by as much as 11% for |m| = 9. Lines (|m| ≤ 3) of the 1-0 and 2-0 bands of HCl broadened by CO₂ were also analyzed in terms of the super-Lorentzian line profile proposed by Varanasi, S. K. Sarangi, and G. D. T. Tejwani (J. Quan. Spectr. Radiative Transfer12, 857 (1972)) and the Lorentzian profile. The results indicate that near the line center (within 3γ), the shape of HCl + CO₂ lines are Lorentzian.     

A complete study of the line intensities of four bands of CO2 around 1.6 and 2.0 μm: A comparison between Fourier transform and diode laser measurements

Atmospheric carbon dioxide is a key specie for the Earth climate. Two spectral windows at 1.6 μm and 2.0 μm are of particular interest for the in situ and remote monitoring of carbon dioxide from satellite, balloon or airborne platforms using infrared absorption spectroscopy. A precise knowledge of the line strengths is a prerequisite for an accurate concentration retrieval. In this paper, we have revisited in the laboratory the (30⁰1)_III←(00⁰0) and (30⁰1)_II ← (00⁰0) bands of CO₂ near 1.6 μm and the (20⁰1)_III ← (00⁰0) and (20⁰1)_II ← (00⁰0) bands near 2.0 μm by implementing both a high-resolution Connes-type Fourier-transform spectrometer and a tunable diode laser spectrometer equipped with several telecommunication-type semiconductor laser devices. Approximately 200 (respectively 18) transitions of CO₂ have been carefully investigated in spectra recorded with the FT spectrometer (respectively with the tunable diode laser spectrometer). The intensity measurements achieved with both instruments are thoroughly compared to previous instrumental determinations, ab-initio calculations and available atmospheric molecular database.     

Combined experimental and theoretical investigation of the CO2 adsorption on LaMnO3+y perovskite oxide

The surface interaction of CO₂ with the perovskite-type oxide LaMnO_3+y has been investigated by means of density functional theory calculations and experimental measurements of adsorption isotherms in the temperature range 298-473 K. A (1 0 0) oriented slab of the cubic structure was used for modeling CO₂ adsorption. The reference unit cell contains alternating LaO⁺ layers and layers; one slab is LaO⁺-terminated and the opposite surface is terminated. A Freundlich isotherm fitted the experimental data satisfactorily. Analysis of the isosteric heat revealed an energetically heterogeneous character for the lanthanum manganite oxide surface, mainly due to the degree of heterogeneity of the adsorption center and due to the adsorbate-adsorbate lateral interactions. Considering theoretical calculations and thermodynamical approaches, two types of active sites were found to be responsible for irreversible and reversible adsorption of CO₂ as a function of surface coverage and O₂ treatment. Strong adsorption takes place on the surface containing La cations. The strongest adsorption is associated with surface oxygen vacancies, center. The next strongest adsorption, a flat adaptation of CO₂ molecules with respect to the surface sites, with a strong binding to a surface oxygen, leads to chemisorbed carbonate species. These adsorption modes are chiefly indicative of a high basic character of the lanthanum manganite oxide surface. Several cationic sites formed by lanthanum and manganese cations are able to weakly adsorb CO₂ molecules in perpendicular or bridged forms. The latter adsorption modes suggest a weak acidic character of the manganite adsorbent.     

CO2 adsorption on Cr(1 1 0) and Cr2O3(0 0 0 1)/Cr(1 1 0)

We attempt to correlate qualitatively the surface structure with the chemical activity for a metal surface, Cr(1 1 0), and one of its surface oxides, Cr₂O₃(0 0 0 1)/Cr(1 1 0). The kinetics and dynamics of CO₂ adsorption have been studied by low energy electron diffraction (LEED), Aug er electron spectroscopy (AES), and thermal desorption spectroscopy (TDS), as well as adsorption probability measurements conducted for impact energies of E_i = 0.1-1.1 eV and adsorption temperatures of T_s = 92-135 K. The Cr(1 1 0) surface is characterized by a square shaped LEED pattern, contamination free Cr AES, and a single dominant TDS peak (binding energy E_d = 33.3 kJ/mol, first order pre-exponential 1 × 10¹³ s⁻¹). The oxide exhibits a hexagonal shaped LEED pattern, Cr AES with an additional O-line, and two TDS peaks (E_d = 39.5 and 30.5 kJ/mol). The initial adsorption probability, S₀, is independent of T_s for both systems and decreases exponentially from 0.69 to 0.22 for Cr(1 1 0) with increasing E_i, with S₀ smaller by ∼0.15 for the surface oxide. The coverage dependence of the adsorption probability, S(Θ), at low E_i is approx. independent of coverage (Kisliuk-shape) and increases initially at large E_i with coverage (adsorbate-assisted adsorption). CO₂ physisorbs on both systems and the adsorption is non-activated and precursor mediated. Monte Carlo simulations (MCS) have been used to parameterize the beam scattering data. The coverage dependence of E_d has been obtained by means of a Redhead analysis of the TDS curves.     

Line shape of the far-wing beyond the band head of the CO2ν3 band

Carbon dioxide is one of the most important trace gases in the terrestrial atmosphere. The spectral data required in remote sensing are the spectral parameter of each absorption line and a line shape model. This paper describes the absorption properties of CO₂ near 2400 cm⁻¹; these properties are of interest to those in the atmospheric temperature sounding field. The shape of the far-wing of N₂- and O₂-broadened CO₂ lines was investigated in the 2200-2500 cm⁻¹ spectral region in a temperature range of atmospheric interest (230-318 K). We focused on the higher rotational quantum number of the R-branch in the ν₃ band, where the effect of the far-wing is enhanced. The effect of the far-wing has been studied extensively by others, since the CO₂ν₃ band is known to exhibit sub-Lorentzian behavior. Here, we show the observed spectra along with calculated spectra for five temperatures. We used first-order line-mixing and the χ-factor, which accounts for the effect of the far-wing, to create the calculated spectra. Our results provide new knowledge of quantum interference of the spectral line in the ν₃ band of CO₂.     

Line strengths of CO2: 4550-7000 cm

Line positions and strengths of ¹²C¹⁶O₂ were measured between 4550 and 7000 cm⁻¹ using near infrared absorption spectra recorded at 0.01-0.013 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory at Kitt Peak, Arizona. These were retrieved from 42 laboratory spectra obtained at room temperature with five absorption cells having various optical path lengths (from 0.1 to 409 m) filled with natural and enriched samples of CO₂ at pressures ranging from 2 to 581 Torr. In all, band strengths and Herman-Wallis-like F-factor coefficients were determined for 58 vibration-rotation bands from the least-squares fits of over 2100 unblended line strengths; strengths of 34 of these bands had not been previously reported. Band strengths in natural abundance generally ranged from 3.30 × 10⁻²⁰ to 2.8 × 10⁻²⁵ cm⁻¹/molecule cm⁻² at 296 K. It was found that the high J transitions (J′ ? 61) of the 20012 ← 00001 band centered at 4977.8347 cm⁻¹ are perturbed, affecting both measured positions and strengths. Two other interacting bands, 21113e ← 01101e and 40002e ← 01101e, were also analyzed using degenerate perturbation theory. Comparisons with corresponding values from the literature indicate that absolute accuracies better than 1% and precisions of 0.5% were achieved for the strongest bands.     

Absorption spectrum of CO2 in the 4.82-μm region

The absorption spectrum of CO₂ in the 4.82-μm region has been observed with a high-resolution spectrometer. The (11¹0, 03¹0)_I-00⁰0 transition and the “hot” transitions (12²0, 04²0)_I-01¹0 and (20⁰0, 04⁰0)_I-01¹0 have been calibrated. The effective rotational constants of the upper levels have been deduced with good accuracy.     

A complete study of CO2 line parameters around 4845 cm for Lidar applications

A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique of Reims (France) to study CO₂ line intensities, self-broadening coefficients and air-pressure-broadening coefficients near 2.063 μm. The spectral region ranging from 4843 to 4848 cm⁻¹, which is suitable for the measurement of atmospheric carbon dioxide (CO₂) mixing ratios was studied using a new generation-commercial diode laser from Nanoplus. Three lines of the (20°1)_III←(0 0 0) band of CO₂ have been studied. The results of intensity measurements and self-broadening coefficients are compared with previous determinations and available databases. Furthermore, the air-broadening coefficients for these transitions are also reported and analyzed. Finally, these new parameters are used for the measurement of atmospheric CO₂ mixing ratio with the 2 μm heterodyne differential absorption Lidar from the Laboratoire de Météorologie Dynamique at Palaiseau (France). These new parameters demonstrate a dramatic improvement of the retrieved atmospheric CO₂ concentrations.