Vibration-internal rotation-rotation Hamiltonian of an asymmetric top molecule with C3v internal rotor

1985 ◽  
Vol 109 (2) ◽  
pp. 374-387 ◽  
Author(s):  
Krishna Mitra ◽  
Pradip N. Ghosh
Keyword(s):  
Internal Rotation ◽  
Asymmetric Top ◽  
Internal Rotor

The asymmetric top–asymmetric frame internal rotation spectrum of ethyl alcohol

2008 ◽  
Vol 251 (1-2) ◽  
pp. 394-409 ◽  
Author(s):  
John C. Pearson ◽  
Carolyn S. Brauer ◽  
Brian J. Drouin
Keyword(s):  
Internal Rotation ◽  
Ethyl Alcohol ◽  
Asymmetric Top ◽  
Rotation Spectrum

The Microwave Spectrum of 4-Methylisothiazole

1991 ◽  
Vol 46 (7) ◽  
pp. 635-638 ◽  
Author(s):  
H.-W. Nicolaisen ◽  
J.-U. Grabow ◽  
N. Heineking ◽  
W. Stahl
Keyword(s):  
Fourier Transform ◽  
Internal Rotation ◽  
Molecular Beam ◽  
Microwave Spectrum ◽  
Coupling Constants ◽  
Fourier Transform Spectrometer ◽  
Methyl Group ◽  
Quadrupole Coupling ◽  
Internal Rotor ◽  
Rotor Axis

The microwave spectrum of 4-methylisothiazole was assigned by means of a pulsed molecular beam microwave Fourier transform spectrometer. Analysis of the spectrum yielded the rotational constants .4 = 7370.642(31) MHz, B = 2515.8461 (30) MHz, C = 1897.2863(33) MHz, a threefold barrier to internal rotation of the methyl group of V3 = 3170.81 (130) GHz≙ 105.7669(430) cm-1, a momentum of inertia of the methyl group of Iα = 3.16769(130) amu · Å2 and an angle between internal rotor axis and principal a-axis of Θ= 5.406(38)°. The nitrogen quadrupole coupling constants were determined to be χ+ = χbb + χcc = 1.4822(14) MHz, χ -= χbb-χcc = - 1.4353(25) MHz and χab= - 3.16(12) MHz.

scholarly journals Impact of nonconvergence and various approximations of the partition function on the molecular column densities in the interstellar medium

2019 ◽  
Vol 627 ◽  
pp. A65 ◽  
Author(s):  
M. Carvajal ◽  
C. Favre ◽  
I. Kleiner ◽  
C. Ceccarelli ◽  
E. A. Bergin ◽  
...  
Keyword(s):  
Partition Function ◽  
Column Density ◽  
Methyl Formate ◽  
Isocyanic Acid ◽  
Methyl Cyanide ◽  
Asymmetric Top ◽  
Function Approximations ◽  
Relative Differences ◽  
Internal Rotor ◽  
Typical Temperature

We emphasize that the completeness of the partition function, that is, the use of a converged partition function at the typical temperature range of the survey, is very important to decrease the uncertainty on this quantity and thus to derive reliable interstellar molecular densities. In that context, we show how the use of different approximations for the rovibrational partition function together with some interpolation and/or extrapolation procedures may affect the estimate of the interstellar molecular column density. For that purpose, we apply the partition function calculations to astronomical observations performed with the IRAM-30 m telescope towards the NGC 7538–IRS1 source of two N-bearing molecules: isocyanic acid (HNCO, a quasilinear molecule) and methyl cyanide (CH3CN, a symmetric top molecule). The case of methyl formate (HCOOCH3), which is an asymmetric top O-bearing molecule containing an internal rotor is also discussed. Our analysis shows that the use of different partition function approximations leads to relative differences in the resulting column densities in the range 9–43%. Thus, we expect this work to be relevant for surveys of sources with temperatures higher than 300 K and to observations in the infrared.

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