H2-broadening coefficients in the ν3 band of CH3D at low temperatures

Using a diode-laser spectrometer, we have measured H₂-broadening coefficients of CH₃D at low temperatures (153.5, 183.5, and 223.5 K) for four lines in the ν₃ band. The collisional widths are obtained by fitting each absorption line with three lineshape models: the Voigt, Rautian, and Galatry profiles. The broadening coefficients are also calculated on the basis of a semiclassical model of interacting linear molecules by considering an atom-atom Lennard-Jones potential in addition to electrostatic contributions. By comparing the broadening coefficients at room and low temperatures the temperature dependence of these broadenings has been determined both experimentally and theoretically.     

Analysis of the Line Profiles of CH3CN for theJ= 5 ← 4 andJ= 6 ← 5 Rotational Transitions

The pressure broadening, pressure shift coefficients, and absolute intensities have been obtained for theJ= 6 ← 5 and theJ= 5 ← 4 absorption lines of acetonitrile CH₃CN at 110 and 92 GHz, respectively. The absorption line shapes have been directly recorded modulating the radiation beam by an optical chopper. In addition to the self-effects, the foreign-broadening coefficients have also been measured for N₂, O₂, and Ar.     

ABSORPTION INTENSITIES, PRESSURE-BROADENING AND LINE MIXING PARAMETERS OF SOME LINES OF NH3 IN THE ν4 BAND

The intensities and foreign gas broadening coefficients of 57 selected lines of the ν₄ band of NH₃ have been measured in the region of 1550 cm^-1 using a high resolution Brucker Fourier transform spectrometer. The line intensities were obtained by using the methods of absorbance at the line center and by fitting Voigt profiles to the measured shapes of the lines. The latter method also provides the collisional widths of the lines. In addition, collision cross relaxation coefficients of O₂ and air foreign gases were measured for 9 doublets of NH₃ in the ν₄ band. The J and K quantum numbers dependencies of pressure-broadening coefficients and line intensities are discussed. The observed air broadening and cross relaxation coefficients were found to be in reasonable quantitative agreement with the concentration-weighted average of the N₂ and O₂ broadening coefficients. The comparison of our present and previous results obtained for the NH₃–H₂, NH₃–air, NH₃–N₂ and NH₃–CO₂ collisions shows an increase of the pressure broadening and cross relaxation coefficients with quadrupole moment of the foreign gas. The analysis of the line intensities was based on the third-order theory of line strengths and yields effective transition moments, vibrational band strengths and correction parameters of the symmetric and antisymmetric partial bands of the fundamental ν₄ band.     

H2-broadening,shifting and mixing coefficients of the doublets in the ν2 and ν4 bands of PH3 at room temperature

The broadening, shifting and mixing coefficients of the doublet spectral lines in the ν₂ and ν₄ bands of PH₃ perturbed by H₂ have been determined at room temperature. Indeed, the collisional spectroscopic parameters: intensities, line widths, line shifts and line mixing parameters, are all grouped together in the collisional relaxation matrix. To analyse the collisional process and physical effects on spectra of phosphine (PH₃), we have used the measurements carried out using a tunable diode-laser spectrometer in the ν₂ and ν₄ bands of PH₃ perturbed by hydrogen (H₂) at room temperature. The recorded spectra are fitted by the Voigt profile and the speed-dependent uncorrelated hard collision model of Rautian and Sobelman. These profiles are developed in the studies of isolated lines and are modified to account for the line mixing effects in the overlapping lines. The line widths, line shifts and line mixing parameters are given for six A₁ and A₂ doublet lines with quantum numbers K = 3n,?(n = 1,?2, …) and overlapped by collisional broadening at pressures of less than 50 mbar.     

Self‐association and hydrogen bonding of propionaldehyde in binary mixtures with water and methanol investigated by concentration‐dependent polarized Raman study and DFT calculations

The Raman spectra of neat propionaldehyde [CH₃CH₂CHO or propanal (Pr)] and its binary mixtures with hydrogen‐donor solvents, water (W) and methanol (M), [CH₃CH₂CHO + H₂O] and CH₃CH₂CHO + CH₃OH] with different mole fractions of the reference system, Pr varying from 0.1 to 0.9 at a regular interval of 0.1, were recorded in the ν(CO) stretching region, 1600–1800 cm⁻¹. The isotropic parts of the Raman spectra were analyzed for both the cases. The wavenumber positions and line widths of the component bands were determined by a rigorous line‐shape analysis, and the peaks corresponding to self‐associated and hydrogen‐bonded species were identified. Raman peak at ∼1721 cm⁻¹ in neat Pr, which has been attributed to the self‐associated species, downshifts slightly (∼1 cm⁻¹) in going from mole fraction 0.9 to 0.6 in (Pr + W) binary mixture, but on further dilution it shows a sudden downshift of ∼7 cm⁻¹. This has been attributed to the low solubility of Pr in W (∼30%), which does not permit a hydrogen‐bonded network to form at higher concentrations of Pr. A significant decrease in the intensity of this peak in the Raman spectra of Pr in a nonpolar solvent, n‐heptane, at high dilution (C = 0.05) further confirms that this peak corresponds to the self‐associated species. In case of the (Pr + M) binary mixture, however, the spectral changes with concentration show a rather regular trend and no special features were observed. Copyright © 2010 John Wiley & Sons, Ltd.     

Pressure broadening coefficients of ν5 fundamental band lines of CH3I at 7 μm measured by diode laser absorption spectroscopy

We have measured the room temperature pressure broadening coefficients, γ, of over 100 lines in five Q-branches of the ν₅ perpendicular band of methyl iodide (¹²CH₃I) using tuneable diode laser absorption spectroscopy. The profiles of individual lines in the ^PQ₂, ^PQ₄, ^PQ₅, ^PQ₆ and ^RQ₃ branches were recorded in a 1 m long White cell and at nitrogen or oxygen pressures up to 15 Torr. The lines were fitted to the Voigt profile to obtain the collision broadened line widths. Within individual Q-branches the broadening coefficients decreased monotonically with increasing J and for nitrogen broadening varied between 0.19 cm⁻¹ atm⁻¹ at low J and 0.12 cm⁻¹ atm⁻¹ at high J. The corresponding oxygen broadening coefficients were approximately 20% smaller. Self broadening coefficients were also measured for several of the Q-branches and found to be up to ∼4 times higher than the corresponding nitrogen broadening values.     

Role of cationic gemini surfactants toward enhanced ninhydrin–tryptophan reaction

In this paper we report the effect of dicationic ‘gemini’ surfactants (CH₃)₂C₁₆H₃₃N⁺? (CH₂)_m? N⁺C₁₆H₃₃(CH₃)₂, 2Br^? (where m = 4, 5, 6) on the reaction of ninhydrin with DL ‐tryptophan. The gemini surfactant micellar media are comparatively more effective than their conventional monomeric counterpart cetyltrimethylammonium bromide (CTAB) micelles. Also, whereas typical rate constant (k_ψ) increase and leveling‐off regions, just like CTAB, are observed with geminis, the latter produce a third region of increasing k_ψ at higher concentrations. These subsequent increases are ascribed to changes in micellar morphologies, consistent with changes in ¹H NMR line widths. Quantitative kinetic analysis of the rate constant–[surfactant] data has been performed on the basis of modified pseudophase model. Copyright © 2007 John Wiley & Sons, Ltd.     

Xe-broadening coefficients of 12CH3D: a test of theoretical line shapes

We present the Xe-broadening coefficients for six lines belonging to the ν₃ band of ¹²CH₃D measured at room temperature with a diode-laser spectrometer. The collisional widths are obtained from least-squares fitting of each absorption line with theoretical line shapes. We used the well-known Voigt profile, the soft and hard collision models considering the collisional narrowing and also line shapes taking into account the speed dependence of the collisional cross-section. The results derived by these different models are compared with each other and with theoretical broadening coefficients. The calculations are based on a semiclassical impact formalism that includes the atom–atom Lennard–Jones potential for CH₃D–Xe interactions in which CH₃D is considered as a linear molecule.     

Pressure-Broadened Linewidth Measurements in the ν2Band of the CH3Radical

Pressure broadening coefficients for an infrared transition of the methyl radical have been measured for the first time. CH₃radicals, generated by pyrolyzing di-tert-butyl peroxide in a flow of either N₂or Ar, were probed using a tunable diode laser and a multipass absorption cell. The Lorentz half-width of theQ(6,6) line of the ν₂band of CH₃at 607.024 cm⁻¹was measured as a function of pressure at 295 K. The broadening coefficients (HWHM) areb(Ar) = 0.0310 ± 0.0012 cm⁻¹atm⁻¹andb(N₂) = 0.0390 ± 0.0020 cm⁻¹atm⁻¹. These coefficients are lower than those for CH₄–Ar, N₂broadening. This may be due to a lower polarizability or smaller effective hard collision diameter for CH₃relative to CH₄.     

Experimental and theoretical study of N2-broadened acetylene line parameters in the ν1 + ν3 band over a range of temperatures

N₂-broadened line widths and N₂-pressure induced line shifts have been measured for transitions in the ν₁?+?ν₃ band of acetylene at seven temperatures in the range 213–333?K to obtain the temperature dependences of broadening and shift coefficients. For the room-temperature spectra the line mixing effects have been also investigated. The Voigt and hard-collision line profile models were used to retrieve the line parameters. All spectra were recorded using a 3-channel tuneable diode laser spectrometer. The line-broadening and line-shifting coefficients as well as their temperature-dependence parameters have been also evaluated theoretically, in the frame of a semi-classical approach based on an exponential representation of the scattering operator, an intermolecular potential composed of electrostatic quadrupole–quadrupole and pairwise atom–atom interactions as well as on exact trajectories driven by an effective isotropic potential.     

One- and two-photon laser optogalvanic spectroscopy of neon in the 570-626 nm region

Eleven two-photon transitions originating from the 2p⁵3s[3/2]₂, 2p⁵3s′[1/2]_o, 2p⁵3s[3/2]₁, and 2p⁵3s′[1/2]₁ states to the 2p⁵4d configuration states have been investigated in the optogalvanic spectrum of neon in the visible region (570-626 nm) for the first time. The two-photon assignments are confirmed by evaluating the temporal evolution, power dependency, and line widths of the optogalvanic signals. The time evolution of the optogalvanic signals for the two-photon transition originating from the metastable 2p⁵3s[3/2]₂ state to the 2p⁵4d′[3/2]₂ state has also been studied at different discharge currents.     

Measurements and calculations of ethylene line-broadening by argon in the ν7 band at room temperature

Argon broadening coefficients are measured for 32 vibrotational lines in the ν₇ band of ethylene at room temperature using a tunable diode-laser spectrometer. These lines with 3 ≤ J ≤ 19, 0 ≤ K_a ≤ 4, 2 ≤ K_c ≤ 19 in the P, Q and R branches are located in the spectral range 919–1023 cm^?1. The fitting of experimental line shapes with Rautian profile provides collisional widths slightly larger than those derived from the Voigt profile. The independent theoretical estimation of these line widths is performed by the semiclassical approach of Robert-and-Bonamy type with exact isotropic trajectories generalized to asymmetric tops. Even with a rough atom–atom intermolecular potential model the calculated values show good agreement with experimental results.     

The 2ν3 band of CH4 revisited with line mixing: Consequences for spectroscopy and atmospheric retrievals at 1.67 μm

This paper presents a study of absorption in N₂-broadened P and R manifolds of the 2ν₃ band of CH₄ near 6000 cm⁻¹ using high resolution laboratory and atmospheric spectra. This region is of prime importance for the retrieval of methane abundances in the Earth's atmosphere using ground-based or space-borne spectrometers. Recent laboratory investigations have been devoted to the methane spectroscopic parameters in this band, motivated by their previous poor knowledge and their increasing use by remote sensing experiments. In the absence of a better model, previous studies have used Voigt line shapes and thus purposely neglected line mixing (LM). In this paper, we first present direct comparisons between measured laboratory spectra and the results of a model which accounts for LM without adjusting any of the spectroscopic parameters. A good agreement is obtained and the results show that LM does have a significant influence on the shapes of P and R manifolds. Hence, most previously observed discrepancies were not due to improper broadening and shifting coefficients but to the neglect of this effect. This also confirms that widths and shifts derived in recent 2ν₃ band studies neglecting LM are “effective” and lack physical meaning, as suggested in a previous work [17] (Frankenberg et al., 2008). In a second step, the conclusions from the laboratory data are tested using ground-based atmospheric solar absorption spectra. The fit residuals obtained confirm the quality of the proposed model and evidence the impact of line mixing on CH₄ atmospheric spectra. The present results also confirm that laboratory and atmospheric spectra can alternatively be accurately modeled neglecting LM and using ad hoc broadening and shifting parameters. Conclusions of this exercise can be drawn from two perspectives. From the point of view of spectroscopy and understanding of processes, accurate line parameters will not be deduced from fits of laboratory measurements unless line-mixing effects are included in the spectral-shape model. In the meantime, and from the point of view of atmospheric retrievals, neglecting LM with suitable effective line parameters is convenient and accurate (within current retrieval uncertainties). Note that this is only true if this approach is not used for total pressures significantly above 1 atm (e.g. Jupiter).     

Multispectrum fits for line mixing in the ν3 band Q branch of methane

First-order line-mixing coefficients and model relaxation matrix element scaling factors have been obtained for allowed transitions in the ν₃ band Q branch of CH₄ broadened by H₂, He, N₂, O₂, Ar, and CH₄. The broadening, shifting, Dicke-narrowing, and line-mixing parameters are determined by simultaneous least-squares fitting of spectra at pressures from 0.014 to 66.66 kPa recorded with a high-resolution difference-frequency laser. These results confirm, improve, and extend a previous analysis of the lower pressure (?13.3 kPa) data [A.S. Pine, J. Chem. Phys. 97 (1992) 773] which yielded averaged coefficients of individually fit spectra where adjacent broadened lines are still partially resolved.     

Dielectric relaxation,modulus behavior and thermodynamic properties in [N(CH3)3H]2ZnCl4

[N(CH₃)₃H]₂ZnCl₄ has been analyzed by X-ray powder diffraction patterns, differential scanning calorimetry and impedance spectroscopy. The [N(CH₃)₃H]₂ZnCl₄ hybrid compound is obtained by slow evaporation at room temperature and found to crystallize in the orthorhombic system with Pnma space group. Five-phase transitions at low temperature were detected by differential scanning calorimetry measurements. The analysis of Nyquist plots has revealed the contribution of three electrically active regions corresponding to the bulk mechanism, distribution of grain boundaries and electrode processes. The dielectric relaxation is described by a non-Debye model. The study of the dielectric constants ?′, ?″ and loss tangent tan (δ) with frequency exhibits a distribution of relaxation times. The complex modulus plots have confirmed the presence of grains and grain boundaries as well as a non-Debye type of relaxation in the material. Thermodynamic parameters such as the free energy for dipole relaxation ΔF, the enthalpy ΔH and the change in entropy ΔS have been determined with the help of the Eyring theory.     

Hydrogen-broadening coefficients in the ν7 band of ethylene at low temperature

H₂-broadening coefficients have been measured for 35 lines of C₂H₄ at 173.2 K in the P, Q, and R branches of the ν₇ fundamental band near 10 μm, using a tunable diode-laser spectrometer. These lines were individually fitted with a Voigt and a Rautian profile to determine their collisional widths. The resulting broadening coefficients, as well as those previously measured at room temperature are compared with values calculated on the basis of a semiclassical model of interacting linear molecules, using an atom-atom Lennard-Jones potential in addition to the weak electrostatic contributions. A satisfactory agreement is obtained for the results at room temperature, but the theoretical results at low temperature are generally smaller than the experimental data. Finally, the temperature dependence of the broadening coefficients has been determined both experimentally and theoretically.     

Spin–orbit coupling in biradicals. 5. Zero-field splitting in triplet dimethylnitrenium,dimethylphosphenium and dimethylarsenium cations

The spin dipole–spin dipole and spin–orbit coupling contributions to the zero-field splitting parameters D and E of [CH₃–N–CH₃]⁺, [CH₃–P–CH₃]⁺, and [CH₃–As–CH₃]⁺ have been calculated from CASSCF(14,14)/cc-pVTZ wave functions and the Breit–Pauli Hamiltonian at T₁ B3LYP/cc-pVTZ optimized geometries. The spin–orbit coupling contributions represent a minor correction for the dimethylnitrenium cation, which has a triplet ground state. They dominate the spin–spin terms by an order of magnitude in the dimethylphosphenium cation and by more than two orders of magnitude in the dimethylarsenium cation, both of which have a singlet ground state. The properties of all these biradicaloids follow expectations based on the simple algebraic 2-in-2 model of biradical structure.     

Measurement of multiplet intensities and noble gas-broadened line widths in the V3-fundamental of methane

Integrated intensity data at 300°K for J-multiplets between P(11)and R(11) in the _{V3-fundamental of ¹²CH4} are presented, along with the intensity of the entire Q-branch, which also encompasses the Q-branch of the _{V3-fundamental of ¹³CH4}. These data, together with theoretical estimates for the intensities of J-multiplets of J > 11, sum up to a value of S_band= 284±14cm^?2atm^?1 at 300°K. This results is in excellent agreement with most of the previously published values for this parameter. Within experimental error, the intensities of the J-multiplets in the _{V3-fundamental do not seem to exhibit the strong anamolies that were characteristic of lines in the 2V3}-band.Line widths have been measured at 100°K, 130°K, 190°K, 250°K, and 300°K for R(0), R(1), and R(2) broadened by He, Ne and Ar. The temperature dependence of the line width is discussed for the three cases of broadening. In neon broadening at 300°K, the ‘effective mean line widths’ for multiplets R(3) through R(11) have also been obtained experimentally; their J-dependence is interpreted using Gordon's theory of line shapes in multiplet spectra.     

1H NMR Spectral Simplification with Achiral and Chiral Lanthanide Shift Reagents. Mexiletine

The 60 MHz ¹H NMR spectra of mexiletine, 1-(2,6-dimethylphenoxy)-2-propanamine, 1, have been studied at 28° in CDCl₃ solution with the achiral reagent, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium(III), 2, Eu(FOD)₃, and the chiral reagents tris[3-(trifluoromethylhydroxymethylene)-d-camphorato]europium(III), 3, Eu(FACAM)₃, and tris[3-(heptafluoropropylhydroxymethylene)-d-camphorato]europium(III), 4, Eu(HFC)₃. Substantial lanthanide-induced shifts were seen for the proton signals of 1 with each reagent. Appreciable enantiomeric shift differences were seen for both methyl signals and for each of the CH₂CH proton signals using 3 and 4 that should permit direct determinations of enantiomeric excess for samples of 1. A predominant conformation for 1 is suggested based on observed splittings of the CH₂ proton signals and their relative lanthanide-induced shifts.     

Diode-laser measurements and calculations of N2-broadening coefficients in the ν7 band of ethylene

N₂-broadening coefficients have been measured for 41 lines of C₂H₄ at 173.2 K in the P, Q, and R branches of the ν₇ fundamental band near 10 μm, using a tunable diode-laser spectrometer. These lines were individually fitted with a Voigt and a Rautian profile in order to determine their collisional widths. The resulting broadening coefficients, as well as those previously measured at room temperature for 35 transitions, are compared with values calculated on the basis of a semiclassical model of interacting linear molecules, using an atom-atom Lennard-Jones potential in addition to the electrostatic contributions. An overall satisfactory agreement is obtained for all the results at room and low temperatures. Finally the temperature dependence of the broadening coefficients has been determined through the temperature exponent n, experimentally for the 23 common transitions as well as theoretically for all the studied transitions.