View in EDS

The ν17 band of C2H5D from 770 to 880 cm−1.

Saved in:

Bibliographic Details
Title:	The ν17 band of C2H5D from 770 to 880 cm−1.
Authors:	Daly, Adam M.¹ adaly@email.arizona.edu, Drouin, Brian J.¹, Pearson, John C.¹, Sung, Keeyoon¹, Brown, Linda R.¹ Linda.R.Brown@jpl.nasa.gov, Mantz, Arlan², Smith, Mary Ann H.³
Source:	Journal of Molecular Spectroscopy. Oct2015, Vol. 316, p1-10. 10p.
Subjects:	Hydrocarbons, Ethanes, Fourier transform spectrometers, Deuterium, Least squares, Ground state energy
Abstract:	Atmospheric investigations rely heavily on the availability of accurate spectral information of hydrocarbons. To extend the ethane database we recorded a 0.0028 cm − 1 resolution spectrum of 12 C 2 H 5 D from 650 to 1500 cm − 1 using a Bruker Fourier Transform spectrometer IFS-125HR at the Jet Propulsion Laboratory. The 98% deuterium-enriched sample was contained in a 0.2038 m absorption cell; one spectrum was obtained with the sample cryogenically cooled to 130.5 K and another at room temperature. From the cold data, we retrieved line positions and intensities of 8704 individual absorption features from 770 to 880 cm − 1 using a least squares curve fitting algorithm. From this set of measurements, we assigned 5035 transitions to the v 17 fundamental at 805.342729(27) cm − 1 ; this band is a c-type vibration, with often-resolved A and E components arising from internal rotation. The positions were modeled to a 22 term torsional Hamiltonian using SPFIT to fit the spectrum to a standard deviation of 7 × 10 − 4 cm − 1 (21 MHz). The prediction of the 5035 line intensities at 130.5 K agreed with observed intensities, but a small centrifugal distortion type correction to the transition dipole was needed to model the intensity of high K a R and P transitions. The integrated band intensities of 3.6628 × 10 − 19 cm − 1 /(molecule cm − 2 ) at 296 K in the 770–880 cm − 1 region was obtained. To predict line intensities at different temperatures, the partition function values were determined at nine temperatures between 9.8 and 300 K by summing individual energy levels up to J = 99 and K a = 99 for the six states up through ν 17 at 805 cm − 1 . We found the energy of A and E are inverted as compared to ground state (with the E state lower than the A state) and the splitting, −241.8(10) MHz, lies between the ground state value of +74.167(18) MHz and the first torsional state (ν 18 = 271.1 cm − 1 ) value of −3382.23(34) MHz. The proximity of the energy splitting to the ground state suggests that the ν 17 state has a similar torsional character. The resulting prediction of singly-deuterated ethane absorption at 12.5 μm enables its detection in planetary atmospheres, including those of Titan and exoplanets. [ABSTRACT FROM AUTHOR]
	Copyright of Journal of Molecular Spectroscopy is the property of Academic Press Inc. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database:	Engineering Source

Description
Abstract:	Atmospheric investigations rely heavily on the availability of accurate spectral information of hydrocarbons. To extend the ethane database we recorded a 0.0028 cm − 1 resolution spectrum of 12 C 2 H 5 D from 650 to 1500 cm − 1 using a Bruker Fourier Transform spectrometer IFS-125HR at the Jet Propulsion Laboratory. The 98% deuterium-enriched sample was contained in a 0.2038 m absorption cell; one spectrum was obtained with the sample cryogenically cooled to 130.5 K and another at room temperature. From the cold data, we retrieved line positions and intensities of 8704 individual absorption features from 770 to 880 cm − 1 using a least squares curve fitting algorithm. From this set of measurements, we assigned 5035 transitions to the v 17 fundamental at 805.342729(27) cm − 1 ; this band is a c-type vibration, with often-resolved A and E components arising from internal rotation. The positions were modeled to a 22 term torsional Hamiltonian using SPFIT to fit the spectrum to a standard deviation of 7 × 10 − 4 cm − 1 (21 MHz). The prediction of the 5035 line intensities at 130.5 K agreed with observed intensities, but a small centrifugal distortion type correction to the transition dipole was needed to model the intensity of high K a R and P transitions. The integrated band intensities of 3.6628 × 10 − 19 cm − 1 /(molecule cm − 2 ) at 296 K in the 770–880 cm − 1 region was obtained. To predict line intensities at different temperatures, the partition function values were determined at nine temperatures between 9.8 and 300 K by summing individual energy levels up to J = 99 and K a = 99 for the six states up through ν 17 at 805 cm − 1 . We found the energy of A and E are inverted as compared to ground state (with the E state lower than the A state) and the splitting, −241.8(10) MHz, lies between the ground state value of +74.167(18) MHz and the first torsional state (ν 18 = 271.1 cm − 1 ) value of −3382.23(34) MHz. The proximity of the energy splitting to the ground state suggests that the ν 17 state has a similar torsional character. The resulting prediction of singly-deuterated ethane absorption at 12.5 μm enables its detection in planetary atmospheres, including those of Titan and exoplanets. [ABSTRACT FROM AUTHOR]
ISSN:	00222852
DOI:	10.1016/j.jms.2015.06.006