Unitless Standard Deviation Research Articles

Line Position and Line Intensity Modelings of H218O up to the First Triad and J = 20

Line position and line intensity analyses are carried out for the H218O isotopic species of the water molecule. Both datasets involve the five lowest lying vibrational states. For the line position analysis, the dataset includes infrared and far infrared transitions recorded in this work using high-temperature Fourier transform emission spectroscopy. Also included are already published infrared, far infrared, microwave, terahertz, Doppler-free combination differences, and kHz accuracy lines. The fitting is carried out with the bending–rotation approach and allows us to reproduce 12 858 line positions involving levels with J ≤ 20 and Ka ≤ 18, with a unitless standard deviation of 1.9, varying 207 spectroscopic parameters. For the line intensity analysis, far infrared line intensities measured in this work using Fourier transform spectroscopy in addition to previously measured line intensities are fitted. 5612 line intensities are accounted for with a unitless standard deviation of 1.5. The results from both analyses are used to build a line list for atmospherical purposes, spanning the 2–5000 cm−1 spectral range and containing 7593 lines. This line list and calculated energies and line intensities are compared to those already published.

Tunneling motion and splitting in the CH2OH radical: (Sub-)millimeter wave spectrum analysis.

The (sub-)millimeter wave spectrum of the non-rigid CH2OH radical is investigated both experimentally and theoretically. Ab initio calculations are carried out to quantitatively characterize its potential energy surface as a function of the two large amplitude ∠H1COH and ∠H2COH dihedral angles. It is shown that the radical displays a large amplitude torsional-like motion of its CH2 group with respect to the OH group. The rotation-torsion levels computed with the help of a 4D Hamiltonian accounting for this torsional-like motion and for the overall rotation exhibit a tunneling splitting, in agreement with recent experimental investigations, and a strong rotational dependence of this tunneling splitting on the rotational quantum number Ka due to the rotation-torsion Coriolis coupling. Based on an internal axis method approach, a fitting Hamiltonian accounting for tunneling effects and for the fine and hyperfine structure is built and applied to the fitting of the new (sub)-millimeter wave transitions measured in this work along with previously available high-resolution data. 778 frequencies and wavenumbers are reproduced with a unitless standard deviation of 0.79 using 27 parameters. The N = 0 tunneling splitting, which could not be determined unambiguously in the previous high-resolution investigations, is determined based on its rotational dependence.

The rotation-torsion spectrum of CD2HOH

New transitions are reported in the submillimeter wave, terahertz, and far-infrared rotation-torsion spectrum of doubly-deuterated methanol CD2HOH. The newly assigned transitions allow us to spectroscopically characterize torsional states with 0⩽K⩽12 and 0⩽vt⩽2. Three line position analyses are carried out. In the first one, restricted to rotation-torsion lines involving torsional states with 3⩽K⩽12 and vt⩽2, rotational energies are evaluated with a J(J+1) Taylor-type expansion for each torsional state. 4853transitions were accounted for with a unitless standard deviation of 11.4. In the second analysis, 126torsional subband centers are fitted to obtain refined torsional parameters including the hindering potential. In the third analysis, 5911rotation-torsion transitions involving torsional states with vt⩽2, and J⩽26 are reproduced with a unitless standard deviation of 3.2 using a four-dimensional rotation-torsion fitting Hamiltonian.

Extreme anomalous centrifugal distortion in methylene.

A new treatment is presented to account for the extreme anomalous centrifugal distortion displayed by the open-shell methylene radical. This new treatment is based on a four-dimensional approach in which both the overall rotation and the large amplitude bending mode are treated simultaneously. It accounts for the spin-rotation and spin-spin fine couplings, assumed to depend on the large amplitude bending coordinate, as well as for the hyperfine coupling. The new treatment is tested analyzing the available high-resolution data. 336 transitions, involving the ground and first excited vibrational states of the bending mode, are reproduced with a unitless standard deviation of 1.3, using 42 molecular constants. Compared to a previous analysis [S. Brünken et al., J. Chem. Phys. 123, 164315 (2005)], the present analysis is more satisfactory as it accounts for a larger dataset and the ratio of the number of data to the number of varied constants is larger. The present theoretical treatment also allows us to retrieve the bending potential and the main kinetic energy term.

Astrophysical detections and databases for the mono deuterated species of acetaldehyde CH2DCOH and CH3COD

Context. Detection of deuterated species may provide information on the evolving chemistry in the earliest phases of star-forming regions. For molecules with two isomeric forms of the same isotopic variant, gas-phase and solid-state formation pathways can be differentiated using their abundance ratio. Aims. Spectroscopic databases for astrophysical purposes are built for the two mono deuterated isomeric species CH2DCOH and CH3COD of the complex organic molecule acetaldehyde. These databases can be used to search and detect these two species in astrophysical surveys, retrieving their column density and therefore abundances. Methods. Submillimeter wave and terahertz transitions were measured for mono deuterated acetaldehyde CH2DCOH which is a non-rigid species displaying internal rotation of its asymmetrical CH2D methyl group. An analysis of a dataset consisting of previously measured microwave data and the newly measured transition was carried out with a model accounting for the large amplitude torsion. Results. The frequencies of 2556 transitions are reproduced with a unitless standard deviation of 2.3 yielding various spectroscopic constants. Spectroscopic databases for astrophysical purposes were built for CH2DCOH using the results of the present analysis and for CH3COD using the results of a previous spectroscopic investigation. These two species were both searched for and are detected toward a low-mass star-forming region. Conclusions. We report the first detection of CH2DCOH (93 transitions) and the detection of CH3COD (43 transitions) species in source B of the IRAS 16293−2422 young stellar binary system located in the ρ Ophiuchus cloud region, using the publicly available ALMA Protostellar Interferometric Line Survey.

Experimental and theoretical investigations of H2O-Ar.

We have used continuous-wave cavity ring-down spectroscopy to record the spectrum of H2O-Ar in the 2OH excitation range of H2O. 24 sub-bands have been observed. Their rotational structure (Trot = 12 K) is analyzed and the lines are fitted separately for ortho and para species together with microwave and far infrared data from the literature, with a unitless standard deviation σ=0.98 and 1.31, respectively. Their vibrational analysis is supported by a theoretical input based on an intramolecular potential energy surface obtained through ab initio calculations and computation of the rotational energy of sub-states of the complex with the water monomer in excited vibrational states up to the first hexad. For the ground and (010) vibrational states, the theoretical results agree well with experimental energies and rotational constants in the literature. For the excited vibrational states of the first hexad, they guided the assignment of the observed sub-bands. The upper state vibrational predissociation lifetime is estimated to be 3 ns from observed spectral linewidths.

Overtone, 2OH spectroscopy of H2O[sbnd]Kr

We have used continuous-wave cavity ring-down spectroscopy to record the spectrum of H2OKr in the 2OH excitation range of H2O. 11 sub-bands have been observed for the main krypton isotope, 84Kr. Their rotational structure (Trot=18K) is analyzed and the lines fitted together with literature microwave data, with a unitless standard deviation σ=0.86 and 1.32 for ortho and para species, respectively. 4 more sub-bands are observed for the three other isotopes and are also analyzed. The upper state vibrational predissociation lifetime is estimated to 4ns from observed spectral linewidths.

The bending potential energy function of HDO obtained from high-resolution data

Line position and line intensity analyses of the high-resolution spectrum of the HDO isotopic species of the water molecule are performed with an extended version of the Bending-Rotation approach up to the (010) state and J=22. The line position analysis involves 3992 microwave, far infrared and infrared lines, and 421 experimental energy levels which were reproduced with a 1.1 unitless standard deviation. The data set considered in the line intensity analysis consists of 1405 infrared absorpon lines and 4 Stark coefficients fitted with a 1.2 unitless standard deviation. The results of both analyses are compared with previous investigations and are used to build a spectroscopic database which is compared with other available databases and should be useful for interpreting measurements carried out with the Infrared Atmospheric Sounding Interferometer (IASI).

Line position and line intensity analyses of the high-resolution spectrum of H218O up to the First Triad and [formula omitted

Line position and line intensity analyses of the high-resolution spectrum of the H218O isotopic species of the water molecule are performed with the Bending-Rotation approach up to J=17 and the First Triad of interacting states, (020), (100), and (001). The line position analysis involves microwave and terahertz transitions, ground state combination differences, far infrared and infrared lines, and experimental energy levels which were reproduced with a 1.2 unitless standard deviation. The data set considered in the line intensity analysis consists of 3707 infrared transitions recorded using absorption spectroscopy at room temperature which were fitted with a 1.4 unitless standard deviation. The results of both analyses are compared with previous investigations and are used to build a line position and line intensity database to update the HITRAN and GEISA databases. A comparison with the HITRAN 2012 database reveals that the new database yields intensity values closer to the experimental ones.

Analysis of the microwave, terahertz, and far infrared spectra of monodeuterated methanol CH2DOH up to J = 26, K = 11, and o1

The first theoretical approach aimed at accounting for the energy levels of a non-rigid molecule displaying asymmetric-top asymmetric-frame internal rotation is developed. It is applied to a line position analysis of the high-resolution spectrum of the non-rigid CH2DOH molecule and allows us to carry out a global analysis of a data set consisting of already available data and of microwave and far infrared transitions measured in this work. The analysis is restricted to the three lowest lying torsional levels (e0, e1, and o1), to K ⩽ 11, and to J ⩽ 26. For the 8211 fitted lines, the unitless standard deviation is 2.4 and 103 parameters are determined including kinetic energy, hindering potential, and distortion effects parameters.

The submillimeter-wave spectrum of the doubly deuterated species of methyl formate HCOOCD2H

Context. Astronomical surveys of interstellar molecules, such as those that will be available with the very sensitive ALMA telescope, require preliminary laboratory investigations of the microwave and submillimeter-wave spectra of new molecular species to identify these in the interstellar media. Aims: We build a linelist that should allow us to detect HCOOCD2H, provided it is present in the interstellar media in a suitable concentration. Methods: The experimental spectra of HCOOCD2H have been recorded in the microwave and submillimeter-wave energy range. Line frequencies were analyzed using an internal axis method-like treatment taking into account the CD2H internal rotation. Results: 5933 lines of HCOOCD2H have been assigned and their frequencies were reproduced with a unitless standard deviation of 1.6. A linelist with calculated frequencies and intensities was built and spans the 50 - 660 GHz spectral region. The frequency accuracy is better than 0.1 MHz. Conclusions: The pure rotation spectrum of the CD2H-methyl formate isotopolog (HCOOCD2H) has been observed in laboratory for the first time. Tables 3, 6, and 10 are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/543/A46

GLOBAL ASSIGNMENT AND EXTENSION OF MILLIMETER- AND SUBMILLIMETER-WAVE SPECTRAL DATABASE OF 13 C 1 -METHYL FORMATE (H 13 COOCH 3 ) IN THE GROUND AND FIRST EXCITED STATES

A compilation of the available spectroscopic millimeter- and submillimeter-wave data of the ground and first excited states of 13C1-methyl formate (H13COOCH3) has been carried out. The exhaustive analysis of the available transition lines of H13COOCH3 has led to the assignment of 7457 spectral lines by means of a global fit of 45 parameters, using the Rho-Axis Method and the BELGI-Cs code, with a resulting unitless standard deviation of 0.57. Over 1600 lines are included for the first time in the fit. In addition, the line strengths of spectral lines are also calculated using the most recent experimental measurement of the electric dipole moment. In conclusion, the present study represents a notable improvement with respect to previous H13COOCH3 spectral analyses. Therefore, the better accuracy of the present analysis may help the future identification of new H13COOCH3 lines in the interstellar and circumstellar media, and may contribute to decrease some of the spectral confusion due to these species in astronomical surveys.

The microwave spectrum of the mono deuterated species of methyl formate [formula omitted

The microwave spectrum of mono deuterated methyl formate ( HCOOCH 2 D ) was measured in three regions by Fourier transform microwave spectroscopy, conventional Stark modulation techniques, and submillimeter wave spectroscopy. Effects due to the large amplitude torsional motion of the partially deuterated CH 2 D methyl group were evidenced and lead to two sets of transitions. Both sets display a rigid-rotator behavior. In one of them, a small tunneling splitting ranging from 0 to 20 MHz was observed. This splitting was accounted for using a phenomenological IAM-like treatment accounting for its rotational dependence. This model was used to analyze line frequencies of the 1388 measured microwave lines. The unitless standard deviation of the fit is 1.5 and the spectroscopic parameters obtained are consistent with the structure of the molecule and the nature of the large amplitude tunneling motion.

The H 216O molecule: Line position and line intensity analyses up to the second triad

Accurate line strengths were obtained for the H 2 16O molecule in the 800–1750 cm −1 region. Measurements were carried out for 974 lines including pure rotational transitions and ν 2 , 2 ν 2 - ν 2 , 3 ν 2 - 2 ν 2 , and ν 1 - ν 2 band transitions. The absolute experimental uncertainty on the measurements, in percent of the observed line strength, is 1.5% or better for a number of lines. Line position and line intensity analyses of data pertaining to water and involving the eight first vibrational states of this molecule were also carried out. The data considered in the line position analysis were taken from the literature and involved rotational energy levels, line positions, and microwave frequencies. The data considered in the line intensity analysis involve the line strengths measured in this work, line strengths available from the literature, and Stark coefficients. The theoretical model used in both analyses accounts for anomalous centrifugal distortion effects. The unitless standard deviation achieved in both analyses is 1.2.

Isotopically invariant analysis of vibration–rotation transitions of HBr and its isotopologues

The vibration–rotation transition frequencies of HBr and its isotopologues reported in the literature were simultaneously analyzed in a least-squares fit to determine isotopically invariant molecular parameters U kl and Born–Oppenheimer breakdown parameters Δ kl . A total of 692 lines was fitted to Watson’s expression involving 25 adjustable parameters to a weighted unitless standard deviation of σ ≈ 0.91. From new data in the far-infrared region and those of improved precision in the mid-infrared and the near-infrared region, the breakdown parameters for the bromine atom were determined; the parameter Δ 10 Br for the harmonic frequency improved the fit and Δ 01 Br for the rotational constant enabled us to obtain the information on the adiabatic correction to the Born–Oppenheimer approximation.

Global fit of rotational transitions of methyl formate (HCOOCH 3) in the ground and first excited torsional states

The microwave spectrum of methyl formate (HCOOCH 3) has been observed in the frequency range from 7 to 200 GHz. New 348 lines were assigned to E-species in the first excited torsional state. By combining these lines with previously reported data, a global analysis of A- and E-species lines of the ground and first excited torsional states were carried out on the basis of the internal axis method. A total of 3862 transitions were fitted to a Hamiltonian model involving 69 molecular parameters to a weighted unitless standard deviation of 1.96.

The Microwave Spectrum of Acetamide (CH 3CONH 2) in the Frequency Range from 12 to 200 GHz

The microwave spectrum of acetamide (CH 3CONH 2) has been observed in the frequency range from 12 to 200 GHz. New 318 lines in the ground torsional state were assigned and analyzed together with previously reported lines on the basis of the internal axis method. A total of 430 lines were fitted to a weighted unitless standard deviation of 1.7, and molecular parameters were determined.

Reinvestigation of the Microwave Spectrum of Acetamide

About 50 jet-cooled Fourier transform lines for acetamide have been recorded using a new version of our spectrometer, which has been upgraded with a heated nozzle and an expanded automatic scanning range. Nuclear quadrupole hyperfine structure arising from the nitrogen atom was removed theoretically to yield hyperfine-free center frequencies. In addition, about 30 millimeter measurements were carried out. When hyperfine structure was observed for these lines, it was also removed theoretically. A set of 115 A-species and E-species rotational transitions in the torsional ground state, obtained by combining our new measurements with the literature data, have been fit to a model involving 28 torsion, rotation, and torsion–rotation interaction parameters to near experimental uncertainty (i.e., to a weighted unitless standard deviation of 1.5), significantly improving on previous fits. Various theoretical problems associated with K labels for E-species levels in this very low barrier molecule are briefly discussed and used to justify a variant of the signed Ka labels frequently used for internal-rotor E states.

Analysis of the Rotational Levels of Water and Determination of the Potential Energy Function for the Bending ν 2 Mode

A theoretical approach suitable for the calculation of the rovibrational energy levels of water taking into account the anomalous centrifugal distortion displayed by this molecule is presented. In agreement with a previous investigation (L. H. Coudert, J. Mol. Spectrosc. 154, 427-442, 1992), a four-dimensional vibration-rotation Hamiltonian is constructed in which the large-amplitude bending ν 2 Mode and the three degrees of freedom corresponding to the overall rotation of the molecule are considered simultaneously. However, the potential energy function adopted in the present approach displays a physically much more satisfactory behavior than that used in the previous investigation. After introducing phenomenological distortion terms, this Hamiltonian is used to carry out three analyses of already published data and to determine this potential energy function. In the first analysis, the rotational levels belonging to the ground vibrational state (J.-M. Flaud et al., Mol. Phys. 32, 499-521, 1976) are fitted with a unitless standard deviation of 2.4 using 36 model parameters. In the second analysis, the rotational levels belonging to the v 2 = 1 state (C. Camy-Peyret et al., Mol. Phys. 33, 1641-1650, 1977) are fitted for J ≤ 24 with a standard deviation of 2.3 using 31 parameters. In the last analysis, microwave and infrared data corresponding to rotational transitions within the ground vibrational state are fitted with a standard deviation of 1.1 using 36 parameters.