Vibration-rotation Lines Research Articles

Photoacoustic detection of NH3 in power plant emission with a CO2 laser

The paper describes a photoacoustic spectrometer for detection of NH3 in power plant emission with a detection limit below 1 ppm. The radiation source is a tunable CO2 waveguide laser, and detection is performed at reduced pressure, where the vibration-rotation lines of NH3 are essentially Doppler broadened. Immunity against interference is ensured by recording a characteristic spectral profile, and problems associated with the high concentration of CO2, and the associated line center absorption are eliminated by utilizing the effect of kinetic cooling on the photoacoustic phase. A computerized spectrometer has been constructed and tested under realistic conditions at a Danish power plant operating a test facility for selective non-catalytic reduction of NO x . Results of this field test are given.

Diode laser kinetic measurements of vibrational rotational and translational temperatures of CO in CO 2 laser-excited SF 6

The time-resolved diode laser spectroscopic method was applied to the characterization of pulsed CO 2 laser-excited SF 6. The transient signals of rotation-vibration lines of CO, which was added to the system as monitor gas, were observed and dynamic changes of vibrational, rotational and translational temperatures ( T V, T R and T T) of CO were obtained. The T R and T T of CO increased within 30 μs after the CO 2 laser shot, while the T V of CO increased gradually in the time range of 0–1 ms at 1 Torr of SF 6. The rise rate of T R was determined to be (1.0±0.1) × 10 5 s −1 Torr −1 from measurements in various pressures of SF 6, and the result was explained by V-T, R energy transfer in highly excited SF 6. The temperature determined from energy absorption measurements was compared with the T R of CO.

Reduction of the optically pumped molecular laser output with increased pump intensity

It has been found that, beyond a certain point, the optically pumped molecular laser output decreases with increasing pump intensity. This reduction phenomenon may be attributed to the optical nonlinear processes. The use of such laser behaviour for tuning through vibrational-rotational lines has been demonstrated. The possibility of pump-intensity-driven polarization control has been shown experimentally.

An infrared spectroscopic search for the molecular ion H3(+)

view Abstract Citations (37) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Infrared Spectroscopic Search for the Molecular Ion H 3 + Geballe, T. R. ; Oka, T. Abstract The molecular ion H3(+) is thought to play a fundamental role in the chemistry of the interstellar medium. Here, a search for infrared vibration-rotation lines of H3(+) at 4 microns toward five obscured infrared objects is reported. Upper limits corresponding to H3+ column densities of (4-10) x 10 to the 14th/sq cm are found. Publication: The Astrophysical Journal Pub Date: July 1989 DOI: 10.1086/167641 Bibcode: 1989ApJ...342..855G Keywords: Hydrogen Ions; Infrared Spectroscopy; Interstellar Chemistry; Molecular Ions; Interstellar Matter; Line Spectra; Molecular Clouds; Rotational Spectra; Vibrational Spectra; Astrophysics; INTERSTELLAR: ABUNDANCES; INTERSTELLAR: MOLECULES; LINE IDENTIFICATIONS full text sources ADS | data products SIMBAD (8)

Absolute infrared transition moments for open shell diatomics from J dependence of transition intensities: Application to OH

A general approach to the determination of the dipole moment function and of the absolute vibrational transition moments for diatomic molecules is presented. This method utilizes the variation of intensity with J within a vibrational transition, together with permanent dipole moment information, to extract the absolute transition moments. An essential feature of the model is its use of algebraic expressions for calculating vibration–rotation line intensities. These expressions can be rapidly evaluated in a least squares fit which determines the dipole moment function. This approach is general in that it is not limited to 1Σ state molecules, nor to the simplest of Hund’s case couplings of spin, orbital and mechanical angular momentum. It is also not limited to molecules with essentially linear dipole moment functions. The model is successfully applied to the OH molecule which violates each of these restrictions. In the accompanying work we report experimental measurements of relative infrared absorption intensity measurements for OH v=1←0 transitions and the extraction of an experimental μ(r) using the approach presented here.

A new analysis of the vibration-rotation spectrum of CH from solar spectra

In the solar spectrum, CH vibration-rotation lines are excited to higher vibrational and much higher rotational quantum numbers than in any laboratory source. We have observed, for the first time, a very large number of new lines (1-0 and 2-1 up to J = 34.5, 3-2 up to J = 31.5, and even 4-3, never seen before, up to J = 24.5) on solar spectra obtained from space, with the ATMOS-SL3 instrument. A total of 558 lines have been used to derive new accurate molecular constants for the X 2Π ground state of CH.

The line intensities of the H 218O molecule first hexad interacting vibrational states

The 693 vibration-rotation line intensities of the H 2 18O molecule first hexad interacting vibrational states have been fitted for determining the parameters of the transformed dipole moment. The experimental data (J.-P. Chevillard, J.-Y. Mandin, C. Camy-Peyret, and J.-M. Flaud, Canad. J. Phys. 64, 746–761 (1986)) and the rotational constants (O. N. Ulenikov and A. S. Zhilyakov, J. Mol. Spectrosc. 133 (1989)) were used as the initial data. The parameters obtained from the fitting reproduce the experimental line intensities with an average accuracy of 6–8%.

Dipole moments of laser transitions of isotopic carbon dioxide. experiment and theory

Absorption measurements have been made for vibration-rotation lines of the [10 00, 02 00] I-00 01 (long wavelength, I) and [10 00, 02 00] II-00 01 (short wavelength, II) transitions of four symmetric, isotopic species of carbon dioxide ( 12C 16O 2, 13C 16O 2, 12C 18O 2, and 13C 18O 2). The derived rotationless dipole moments of I and II have the following values (in 10 -4 D): 376 ± 2 and 325 ± 2 ( 12C 16O 2), 413 ± 3 and 238 ± 3 ( 13C 16O 2), 297 (calculated value) and 397 ± 2 ( 12C 18O 2), 342 ± 6 and 357 ± 6 ( 13C 18O 2), respectively. The calculated matrix elements relating to changes in both wave functions and electrooptical constants resulting from isotope substitution agree with the experimental data within 4%. The results obtained are used to analyse the properties of CO 2 isotopic lasers.

Influence of SF6on the energy characteristics of an H2–F2chemical laser

A model of a hydrogen fluoride laser taking into account the finite rate of rotational relaxation is used to study the influence of the addition of SF6 to the mixture on the energy characteristics of a pulsed H2–F2 chemical laser. A comparison between the results of the calculations and the experimental data suggests that an increase in the laser energy with increasing SF6 concentration in the active mixture is largely due to a rise in the rate of rotational relaxation of the HF molecules. It is shown that a drop in the specific laser output energy at very high SF6 concentrations is not only due to an increase in the rate of vibrational–rotational relaxation, but also to the influence of the resonator threshold on the laser energy characteristics as a result of the appreciable broadening of the HF vibrational–rotational lines.

Calculation of the vibration–rotation line intensities in the Raman spectra of gases

AbstractThe method of irreducible tensorial sets is used for deriving general formulae describing the intensities of vibration‐rotation Raman lines of molecules of different symmetries. Using this method, generalization of the parameters characterizing isotropic, antisymmetric scattering, taking into account vibration‐rotation interactions, has been carried out. The effect of vibration‐rotation interactions on the Raman scattering cross‐section is considered.

Ratios of molecular hydrogen line intensities in shocked gas - Evidence for cooling zones

Column densities of molecular hydrogen have been calculated from 19 infrared vibration-rotation and pure rotational line intensities measured at peak 1 of the Orion molecular outflow. The run of column density with energy level is similar to a simple coolng zone model of the line-emitting region, but is not well fitted by predictions of C-shock models current in the literature.

Time autocorrelations of intermolecular interactions and impact broadening of vibration-rotation lines. I. Rotational Raman effect in gaseous hydrogen and deuterium

The second-order perturbation expressions for the Raman vibration-rotation half-widths are derived which can be applied to any dense medium. These are used to deduce the Fourier transform spectra of the anisotropic H 2-H 2 interaction potential from the rotational broadening data on gaseous hydrogen and deuterium. Reliability and accuracy of the solution of this partial inverse problem are obtained by the linear regression analysis. The computer simulations undertaken for room temperature hydrogen reveal the predominant role of the doubly anisotropic quadrupolar forces in the rotational broadening. The computed spectra are shown to be sensitive to the details of the potential surface.

Detection of C 3 in the Circumstellar Shell of IRC+10216

Vibration-rotation lines of C(3) have been identified in the circumstellar spectrum of the obscured carbon star IRC+10216. This molecule is of interest in both the chemistry of flames, where it may be involved in the formation of soot, and in astrophysics, where it is a potential building block for carbonaceous grains. This high-resolution infrared detection of the pure carbon chain molecule C(3) allows the estimation of the equilibrium C-C bond length, 1.297 angstroms. Possible astrophysical formation and destruction mechanisms for C(3) are reviewed, including the relationship between C(3) and carbon clusters.

Vibration-rotation spectroscopy of the HD+ion near the dissociation limit

We have observed and measured five rotational components of the 21–17 band in the HD+ molecular ion. The highest bound rotational level in υ=21 is predicted to be N = 3, which lies only 1·8 cm−1 below the H++D dissociation limit, and we have observed transitions involving all four rotational levels of υ=21. The measured transition frequencies are close to those predicted by recent non-adiabatic calculations. Each vibration-rotation line is split into six hyperfine components, which arise primarily because of Fermi contact interactions with the proton and deuteron nuclei. Analysis of these hyperfine multiplets yields values of the Fermi contact hyperfine constants for the lower and upper states in each vibration-rotation transition. These values show that in υ=17 the electron distribution is essentially symmetric, but in υ=21 it becomes increasingly asymmetric as N increases. The proton Fermi contact hyperfine constant is close to 715 MHz in υ=17, but decreases to only 53 MHz in 21,3. Correspondingly the deuteron hyperfine constant increases from 112 MHz in υ=17 to 213 MHz in 21, 3, which is only slightly less than the free deuterium atom value of 218 MHz. These results demonstrate that in 21, 3 the electron is virtually localized at the deuteron, so that the molecule is perhaps best regarded as a long-range H+…D Langevin complex.

Free jet infrared absorption spectroscopy of the ν3band of MoF6

The ν 3 band of MoF6 is studied at a low rotational and vibrational temperature using a tunable diode laser. More than 500 vibration-rotation lines are measured in the range of 740 to 752cm−1 with a Doppler-limited resolution. The observed spectrum is strongly perturbed by the 2ν 5+ν 6 combination state located at 743·3 cm−1. From less perturbed portion of the spectrum, four spectroscopic constants, ν 3, B 3, Bζ 3, and α 224, are determined for all of the seven Mo isotopic species. Energy level structure of the perturbing state is calculated with molecular parameters transferred from the cubic potential constants of SF6. The observed isotopic and J dependence of the perturbation is found to be consistent with Fermi interactions between the ν 3 and the 2ν 5+ν 6 state.

Transition dipole moment and intensity measurements of the a2 ν2 ← sν2 hot band of 14NH 3

Intensities of more than 30 vibration-rotation lines in the P-, Q-, and R-branch regions of the a2 ν 2 ← sν 2 hot band of 14NH 3 have been measured using a tunable diode laser operating in the region 860–1040 cm −1. For several of the transitions, measurements have been made both by the fast direct method and also by the equivalent width method. From the measured data a value of 0.274(5) has been derived for the transition dipole moment of the 〈1 s| μ|2 a〉 hot band. N 2-broadening coefficients are also reported for a few selected transitions.

Measurements of argon-, helium-, hydrogen-, and nitrogen-broadened widths of methane lines near 9000 cm −1

Pressure-broadened widths of rotational-vibrational lines in CH 4 have been measured at very high spectral resolution in the R-branch of the 3 v 3 overtone. The broadening gases wer Ar, He, H 2, and N 2. Results are presented as averages for J-multiplets at ambient temperature. The overall values in cm −1-atm −1 for these R-branch lines are 0.0651 (CH 4-Ar), 0.0508 (CH[in4]-He), 0.0728 (Ch 4-H 2), and 0.0715 (CH 4-N 2.

A time-resolved tunable diode laser study of the photodissociation dynamics of W(CO) 6

Time-resolved diode laser absorption spectroscopy has been used to study the photodissociation of W (CO) 6 following excitation at 351 nm. The narrow linewidth (≈ 10 −4 cm −1) and tunability of this infrared source allows the nascent rotation-vibrational energy distribution of the CO product to be determined. Additionally, translational energy disposal can be characterized by measurements of the shapes of individual rotation-vibration lines. Our results indicate that energy is partitioned preferentially to product translational and vibrational, rather than rotational, motion for the 351 nm photofragmentation of W(CO) 6.

Theoretical intensities for rotation-vibration lines of water using particles-on-a-sphere wavefunctions

Using variational wavefunctions calculated from the particles-on-a-sphere model, and an ab initio electric dipole moment function, we have calculated intensities for the allowed rotation-vibration transitions involving states with J=0, 1, 2 in the pure rotational, ν 2, and 2ν 2 bands of water. A comparison of our results with experimental and rigid-rotor intensities suggests that our wavefunctions correctly take into account substantial rotation-bending interactions, but run into difficulties for the 2ν 2 band, where the neglected stretch-bend interactions are important.

Temperature estimation of carbon dioxide by infrared absorption spectrometry at medium resolution

A method for estimating the temperature of a sample of CO 2 gas heated above ambient temperature is evaluated. A nonlinear, least-squares regression fir for the peak absorbance of the rotation-vibration lines of the hot bands of CO 2 was obtained for samples at temperatures from 90 to 190°C and at pressures from 200 to 650 torr. The i.r. spectra of CO 2 gas samples in a 1 m cell were collected using a Fourier-transform i.r. spectrometer. The spectral resolution was sufficient to resolve the rotational fine structure of these bands. However, it was necessary to account for the effect of limited instrument resolution in fitting the data. The temperatures retrieved from the regression were compared with the temperature of the sample. Good agreement was obtained between the directly measured temperature and the value determined spectroscopically. The sensitivity of the fitting program to increased noise in the spectrum was also studied.