Precise ro-vibrational analysis of molecular bands forbidden in absorption: The ν8+ν10 band of the 12C2H4 molecule

Abstract Ethylene (ethene, H2C=CH2) is a naturally occurring compound in ambient air that affects atmospheric chemistry and global climate. The C2H4 spectrum is available in databases only for the 1000 and 3000 cm−1 ranges. In this work, the ethylene absorption spectrum was measured in the 6030–6250 cm−1 range with the use of a high resolution Bruker IFS 125HR Fourier-spectrometer and a two-channel opto-acoustic spectrometer with a diode laser. As a secondary standard of wavelengths, the methane absorption spectrum was used in both cases. A preliminary analysis was realized thanks to the tensorial formalism developed by the Dijon group that is implemented in the XTDS software package [39] . We considered the two combination bands ν 5 + ν 9 and ν 5 + ν 11 as an interacting dyad. Parameters for the ν 9 / ν 11 dyad were fitted simultaneously from a re-analysis of previously recorded supersonic expansion jet FTIR data, while parameters for the v5=1 Raman level were taken from literature. More than 600 lines could be assigned in the 6030–6250 cm−1 region (and also 682 in the 2950–3150 cm−1 region) and effective Hamiltonian parameters were fitted, including Coriolis interaction parameters. The dyad features are globally quite well reproduced, even if there are still problems at high J values.

High-Resolution Spectroscopy and Preliminary Global Analysis of C-H Stretching Vibrations of C2H4 in the 3000 and 6000 cm-1 Regions

The high resolution IR spectrum of the CH 2 CD 2 ethylene isotopomer was recorded and analyzed in the region of 1300–1450 cm−1, where the strongly interacting bands ν 12 ( A 1 ) and 2 ν 10 ( A 1 ) are located (the band ν12 was analyzed earlier; transitions belonging to the 2ν10 band were experimentally recorded and assigned in the present study for the first time). For description of the upper ro-vibrational energy levels obtained from the assigned transitions, the used Hamiltonian takes into account not only resonance interactions between the states ( v 12 = 1 ) and ( v 10 = 2 ) , but interactions of the mentioned pair of vibrational states with the states ( v 7 = v 10 = 1 ) and ( v 7 = 2 ) , as well. More than 1960 and 320 transitions with the values J max . = 48 / K a max . = 20 and J max . = 24 / K a max . = 7 were assigned to the bands ν 12 ( A 1 ) and 2 ν 10 ( A 1 ) , respectively. A set of 59 spectroscopic parameters was obtained from a weighted least square fit procedure. This reproduces the 959 and 180 initial upper ro-vibrational energies of the vibrational states ν 12 ( A 1 ) and 2 ν 10 ( A 1 ) used in the fit with a d rms = 1.7 × 10 − 4 cm − 1 and d rms = 2.2 × 10 − 4 cm − 1 , respectively (in this case, only upper energies obtained from unblended and nonsaturated transitions of relatively high intensities have been taken into account). The ground state rotational parameters were improved in comparison with the parameters known in the literature.

Study of the high resolution FTIR spectrum of CH2CD2 in the region of 1300–1450 cm−1: The ν12(A1) and 2ν10(A1) bands

The high-resolution infrared spectrum of C2H2D2-cis ethylene was analyzed in the region of 1280–1400 cm−1, where the strong ν12 band is located. More than 2000 transitions (about three times more than it was made in the preceding studies) were assigned with the maximum values of the upper quantum numbers J max . = 45 and K a max . = 19 ( J max . = 31 and K a max . = 13 in the preceding studies). For the first time, 22 transitions belonging to the 2ν10 weak band were assigned. For description of the assigned transitions (upper ro-vibrational energy levels), the Hamiltonian model was used which takes into account resonance interactions between the vibrational state ( v 12 = 1 ) and three other closely located states: ( v 10 = 2 ) , ( v 8 = v 10 = 1 ) , and ( v 3 = 1 ) . A set of 43 spectroscopic parameters obtained from a weighted least square fit reproduces the initial experimental data (817 upper energy values and more than 2000 transitions) with the d rms = 2.2 × 10 − 4 cm − 1 which is close to experimental uncertainties and considerably better than in prior studies. Ground state rotational and centrifugal distortion parameters were improved on the basis of the IR experimental data of the present study and microwave data from the earlier literature.

Re-analysis of the high resolution FTIR spectrum of C 2 H 2 D 2 -cis in the region of 1280-1400 cm -1

The high resolution spectra of the 13C2H4 molecule was recorded with a Bruker IFS 120 Fourier transform spectrometer and theoretically analyzed in the 1650 − 1800 cm − 1 region of the ν 8 + ν 10 band which is forbidden in absorption. About 1200 experimental transitions with the maximum values of quantum numbers J max . = 34 and K a max . = 17 were assigned to the ν 8 + ν 10 band. On that basis the 516 high accuracy ro-vibrational energies of the (v8=v10=1) vibrational state, as well as energy levels with J ≤ 2 of the ( v 4 = v 8 = 1 ) and ( v 7 = v 8 = 1 ) vibrational states, were determined which then were used as input data in the weighted fit of spectroscopic parameters of the Hamiltonian (strong local resonance interactions of the ν 8 + ν 10 band with the bands ν 4 + ν 8 and ν 7 + ν 8 have been taken into account). A set of 34 vibrational, rotational, centrifugal distortion, and resonance interaction parameters was obtained from the fit. These parameters reproduce positions of about 1200 experimentally recorded and assigned transitions with the rms error d rms = 0.00018 cm − 1 (blended and very weak transitions are not taken into account in that case).

Precise ro-vibrational analysis of molecular bands forbidden in absorption: The ν8+ν10 band of 13C2H4

High accurate, ~ 1 × 10 − 4 cm − 1 , ro-vibrational spectra of the C 2 13 H 4 molecule in the region of 600–1600 cm −1 were recorded with Bruker IFS 120/125 HR Fourier transform interferometers and analyzed in the Hamiltonian model which takes into account Coriolis resonance interactions between all four bands. More than 660, 3870, 2420, and 2550 transitions belonging to the ν 4 , ν 7 , ν 10 , and ν 12 bands were assigned in the experimental spectrum with the maximum values of quantum numbers J max . / K a max . , equal to 38/10, 43/21, 33/16 and 52/18, respectively. To make the ro-vibrational analysis physically more suitable, the initial values of the rotational and centrifugal distortion parameters of the studied bands were theoretically estimated by the use of isotopic relations. On that basis, a set of 55 vibrational, rotational, centrifugal distortion, and resonance interaction parameters was obtained from the fit. They reproduce values of 2934 initial “experimental” ro-vibrational energy levels obtained from nonsaturated unblended lines (more than 9500 assigned transitions of the ν 4 , ν 7 , ν 10 , and ν 12 bands) with the rms error d rms = 0.00014 cm − 1 . Ground state parameters of the C 2 13 H 4 molecule were improved as well.

M. G. Gabona

Papers

High resolution ro-vibrational analysis of interacting bands ν4, ν7, ν10, and ν12 of 13C2H4