The fitting and prediction of vibration-rotation spectra with spin interactions

Pickett, Herbert M.

doi:10.1016/0022-2852(91)90393-o

Cited by 2,119 publications

(1,635 citation statements)

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“…The assignment to a basis state is not necessarily straight forward. Simply picking the largest coefficient from the basis set expansion, equation (2), is one of the strategies offered (EigenSearch=True, LimitSearch=False) but will often be problematic. As a specific example consider a linear molecule in a 3 Π state with rotational constant, B = 1 cm -1 and spin-orbit coupling constant, A = 20 cm -1 .…”

Section: Quantum Number Assignmentmentioning

confidence: 99%

“…Line lists from other sources can be included in the fitting process with different weights as appropriate, such as combining data from microwave and infra-red sources. The program will take a variety of different formats including HITRAN [22] and Pickett's CALPGM suite [2]. It is also possible to specify constraints between parameters using general algebraic expressions, or fit to an introduced variable (see "variables" in the on-line documentation) with other parameters set from this variable.…”

Section: Fitting Spectramentioning

confidence: 99%

“…This ranges from simple undergraduate spectroscopy practicals where the rotational constant of CO is determined from a traditional infrared spectrum to complex cases involving multiple interacting rovibronic states [1], including open shell systems and nuclear hyperfine structure. It is not the first molecular spectroscopy program to be published -Pickett's CALPGM suite [2] has become something of a standard and there are several others available including ASYTOP [3], ASYROTWIN [4], SPECVIEW [5] and JB95 [6]. PGOPHER aims to cover similar ground, but in a much more general and easy-to-use way.…”

Section: Introductionmentioning

confidence: 99%

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PGOPHER: A program for simulating rotational, vibrational and electronic spectra

Western

2017

Journal of Quantitative Spectroscopy and Radiative Transfer

860

590

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. AbstractThe PGOPHER program is a general purpose program for simulating and fitting molecular spectra, particularly the rotational structure. The current version can handle linear molecules, symmetric tops and asymmetric tops and many possible transitions, both allowed and forbidden, including multiphoton and Raman spectra in addition to the common electric dipole absorptions. Many different interactions can be included in the calculation, including those arising from electron and nuclear spin, and external electric and magnetic fields. Multiple states and interactions between them can also be accounted for, limited only by available memory. Fitting of experimental data can be to line positions (in many common formats), intensities or band contours and the parameters determined can be level populations as well as rotational constants. PGOPHER is provided with a powerful and flexible graphical user interface to simplify many of the tasks required in simulating, understanding and fitting molecular spectra, including Fortrat diagrams and energy level plots in addition to overlaying experimental and simulated spectra. The program is open source, and can be compiled with open source tools. This paper provides a formal description of the operation of version 9.1.

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Section: Quantum Number Assignmentmentioning

confidence: 99%

Section: Fitting Spectramentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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PGOPHER: A program for simulating rotational, vibrational and electronic spectra

Western

2017

Journal of Quantitative Spectroscopy and Radiative Transfer

860

590

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“…The JPL database 2 (Pickett 1991;Pickett et al 1998) is now updated (since April 2009) to include both the newly recalculated methyl formate frequencies and their own predictions (Drouin, B.J.). Because of its threefold internal rotation, the methyl group leads to a series of thermally populated torsional levels that are split into two torsional substates with A and E symmetries.…”

Section: Methyl Formate and Isomers Frequenciesmentioning

confidence: 99%

HCOOCH₃as a probe of temperature and structure in Orion-KL

Favre

Despois

Brouillet

et al. 2011

A&A

238

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Context. The Orion Kleinmann-Low nebula (Orion-KL) is a complex region of star formation. Whereas its proximity allows studies on a scale of a few hundred AU, spectral confusion makes it difficult to identify molecules with low abundances. Aims. We studied an important oxygenated molecule, HCOOCH 3 , to characterize the physical conditions, temperature, and density of the different molecular source components. Methyl formate presents strong close rotational transitions covering a wide range of energy, and its emission in Orion-KL is not contaminated by the emission of N-bearing molecules. This study will help in the future 1) to constrain chemical models for the formation of methyl formate in gas phase or on grain mantles and 2) to search for more complex or prebiotic molecules. Methods. We used high-resolution observations from the IRAM Plateau de Bure Interferometer to reduce spectral confusion and to better isolate the molecular emission regions. We used twelve data sets with a spatial resolution down to 1.8 × 0.8 . Continuum emission was subtracted by selecting apparently line-free channels. Results. We identify 28 methyl formate emission peaks throughout the 50 field of observations. The two strongest peaks, named MF1 and MF2, are in the Compact Ridge and in the southwest of the Hot Core, respectively. From a comparison with single-dish observations, we estimate that we miss less than 15% of the flux and that spectral confusion is still prevailing as half of the expected transitions are blended over the region. Assuming that the transitions are thermalized, we derive the temperature at the five main emission peaks. At the MF1 position in the Compact Ridge we find a temperature of 80 K in a 1.8 × 0.8 beam size and 120 K on a larger scale (3.6 × 2.2 ), suggesting an external source of heating, whereas the temperature is about 130 K at the MF2 position on both scales. Transitions of methyl formate in its first torsionally excited state are detected as well, and the good agreement of the positions on the rotational diagrams between the ground state and the v t = 1 transitions suggests a similar temperature. The LSR velocity of the gas is between 7.5 and 8.0 km s −1 depending on the positions and column density peaks vary from 1.6 × 10 16 to 1.6 × 10 17 cm −2 . A second velocity component is observed around 9−10 km s −1 in a north-south structure stretching from the Compact Ridge up to the BN object, and this component is warmer at the MF1 peak. The two other C 2 H 4 O 2 isomers are not detected, and the derived upper limit for the column density is ≤3 × 10 14 cm −2 for glycolaldehyde and ≤2 × 10 15 cm −2 for acetic acid. From the 223 GHz continuum map, we identify several dust clumps with associated gas masses in the range 0.8 to 5.8 M . Assuming that the methyl formate is spatially distributed as the dust is, we find relative abundances of methyl formate in the range ≤0.1 × 10 −8 to 5.2 × 10 −8 . We suggest a relation between the methyl formate distribution and shocks as traced by 2.12 μm H 2 emission.

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“…These were then included in a global fit that also involves the frequency values for the vibrational ground state up to about 6.7 THz from Azzam et al (2013). As for the other isotopic species of hydrogen sulfide (Cazzoli & Puzzarini 2014;Azzam et al 2013), the fitting procedure was carried out with Pickett's SPFIT program (2009;Pickett 1991) employing Watson's S -reduced Hamiltonian in the I r representation (Watson 1977) with each transition weighted proportionally to the inverse square of its experimental uncertainty. In total, 112 distinct frequency lines were used for obtaining 24 distinct constants up to the eighth-order centrifugal-distortion terms (plus one decic constant).…”

Section: Resultsmentioning

confidence: 99%

Rare isotopic species of hydrogen sulfide: the rotational spectrum of H₂³⁶S

Cazzoli

Puzzarini

Gauß

2014

A&A

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The rotational spectrum of the 36 S-bearing isotopologue of hydrogen sulfide (H 2 S) has been investigated for the first time in the 167 GHz−1.6 THz frequency range, thus providing an accurate and reliable set of spectroscopic parameters. The experimental investigation was backed up by state-of-the-art quantum-chemical calculations, which also allowed us to demonstrate the incorrectness of the previously reported spectroscopic constants. The present results are of suitable accuracy to attempt the astrophysical detection of the isotopic species under consideration. Finally, reliable predictions for the spectroscopic constants of other rare isotopologues of H 2 S, namely the mono-and bi-deuterated species containing 33 S and 34 S, are provided.

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The fitting and prediction of vibration-rotation spectra with spin interactions

Cited by 2,119 publications

References 6 publications

PGOPHER: A program for simulating rotational, vibrational and electronic spectra

PGOPHER: A program for simulating rotational, vibrational and electronic spectra

HCOOCH₃as a probe of temperature and structure in Orion-KL

Rare isotopic species of hydrogen sulfide: the rotational spectrum of H₂³⁶S

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The fitting and prediction of vibration-rotation spectra with spin interactions

Cited by 2,119 publications

References 6 publications

PGOPHER: A program for simulating rotational, vibrational and electronic spectra

PGOPHER: A program for simulating rotational, vibrational and electronic spectra

HCOOCH3as a probe of temperature and structure in Orion-KL

Rare isotopic species of hydrogen sulfide: the rotational spectrum of H236S

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Product

Resources

About

HCOOCH₃as a probe of temperature and structure in Orion-KL

Rare isotopic species of hydrogen sulfide: the rotational spectrum of H₂³⁶S