The v17 band of C2H5D from 770 to 880 cm-1

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 (C2H5D)-C-12 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 x 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 x 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 v(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 (v(18) = 271.1 cm(-1)) value of -3382.23(34) MHz. The proximity of the energy splitting to the ground state suggests that the v(17) state has a similar torsional character. The resulting prediction of singly-deuterated ethane absorption at 12.51 mu m enables its detection in planetary atmospheres, including those of Titan and exoplanets. (C) 2015 Elsevier Inc. All rights reserved.