S. Robert

Vibration-rotation pattern in acetylene. II. Introduction of Coriolis coupling in the global model and analysis of emission spectra of hot acetylene around 3 mu m

A high temperature source has been developed and coupled to a high resolution Fourier transform spectrometer to record emission spectra of acetylene around 3 mum up to 1455 K under Doppler limited resolution (0.015 cm(-1)). The nu(3)-ground state (GS) and nu(2)+nu(4)+nu(5) (Sigma(u) (+) and Delta(u))-GS bands and 76 related hot bands, counting e and f parities separately, are assigned using semiautomatic methods based on a global model to reproduce all related vibration-rotation states. Significantly higher J-values than previously reported are observed for 40 known substates while 37 new e or f vibrational substates, up to about 6000 cm(-1), are identified and characterized by vibration-rotation parameters. The 3 811 new or improved data resulting from the analysis are merged into the database presented by Robert et al. [Mol. Phys. 106, 2581 (2008)], now including 15 562 lines accessing vibrational states up to 8600 cm(-1). A global model, updated as compared to the one in the previous paper, allows all lines in the database to be simultaneously fitted, successfully. The updates are discussed taking into account, in particular, the systematic inclusion of Coriolis interaction.

Acetylene, 12C2H2: new CRDS data and global vibration-rotation analysis up to 8600 cm-1

The absorption spectrum of 12C2H2 has been recorded using cavity ringdown spectroscopy and analyzed in the ranges 6000 − 6356 cm−1 and 6667−7015 cm−1. Fourteen new bands have been identified and additional J-lines were assigned in 10 already known bands. These new data, together with the published vibration–rotation absorption lines of 12C2H2 accessing vibrational states up to 8600 cm−1 have been gathered in a database. The resulting set includes 12137 transitions involving 186 different k = l 4 + l 5 sub-states, with l i the angular momentum quantum number associated to the i degenerate bending vibration. These lines have been fitted simultaneously to spectroscopic parameters through J-dependent Hamiltonian matrices exploiting the vibrational polyad or cluster block-diagonalization, in terms of the pseudo-quantum numbers Nr = 5v 1 + 3v 2 + 5v 3 +v 4 +v 5 and Ns = v 1 + v 2 + v 3, also accounting for k and e/f parities and u/g symmetry. Modes 1 and 2 correspond to the symmetric CH and CC stretchings, mode 3 to the antisymmetric CH stretch, and modes 4 and 5 to the trans- and cis-degenerate bendings, respectively. The fit was successfully achieved, with a dimensionless standard deviation of 0.92, leading to the determination of 266 effective vibration-rotation parameters.

Vibration-rotation energy pattern in acetylene: 13CH12CH up to 6750 cm-1.

All known vibration-rotation absorption lines of 13CH12CH accessing levels up to 6750 cm-1 were gathered from the literature. They were fitted simultaneously to J-dependent Hamiltonian matrices exploiting the well known vibrational polyad or cluster block diagonalization, in terms of the pseudo-quantum-numbers Ns=v1+v2+v3 and Nr=5v1+3v2+5v3+v4+v5, and accounting also for l parity and ef symmetry properties. The anharmonic interaction coupling terms known to occur from a pure vibrational fit in this acetylene isotopologue [Robert et al., J. Chem. Phys. 123, 174302 (2005)] were included in the model. A total of 12 703 transitions accessing 158 different (v1v2v3v4v5,l4l5) vibrational states was fitted with a dimensionless standard deviation of 0.99, leading to the determination of 216 vibration-rotation parameters. The experimental data included very weak vibration-rotation transitions accessing 18 previously unreported states, some of them forming Q branches with very irregular patterns.

The bending vibrations in 12C2H2: global vibration–rotation analysis

A total of 3155 vibration–rotation line positions providing accurate information on all known vibration–rotation states up to 3000u2009cm−1 in 12C2H2 were gathered from the literature. An additional 966 lines were assigned on new spectra. The full data set was simultaneously fitted using an appropriate Hamiltonian, with 85 refined parameters. A dimensionless standard deviation equal to 0.86, accounting for 92% of the lines, was achieved. The vibrational transition dipole moment of the υ5u2009=u20091u2009←u2009υ4u2009=u20091 band observed in the far-infrared was estimated to be |μ5←4|u2009=u20090.55 D with 20% accuracy, from absolute intensity measurements for a few Q-branch lines.

Vibration-Rotation Energy Pattern in Acetylene: 13CH12CH up to 10 120 cm-1

All 18,219 vibration-rotation absorption lines of (13)CH(12)CH published in the literature, accessing substates up to 9400 cm(-1) and including some newly assigned, were simultaneously fitted to J-dependent Hamiltonian matrices exploiting the well-known vibrational polyad or cluster block-diagonalization, in terms of the pseudo quantum numbers N(s) = v(1) + v(2) + v(3) and N(r) = 5v(1) + 3v(2) + 5v(3) + v(4) + v(5), also accounting for k = l(4) + l(5) parity and e/f symmetry properties. Some 1761 of these lines were excluded from the fit, corresponding either to blended lines, for about 30% of them, or probably to lines perturbed by Coriolis for the remaining ones. The dimensionless standard deviation of the fit is 1.10, and 317 vibration-rotation parameters are determined. These results significantly extend those of a previous report considering levels below only 6750 cm(-1) [Fayt, A.; et al. J. Chem. Phys. 2007, 126, 114303]. Unexpected problems are reported when inserting in the global fit the information available on higher-energy polyads, extending from 9300 to 10 120 cm(-1). They are tentatively interpreted as resulting from a combination of the relative evolution of the two effective bending frequencies and long-range interpolyad low-order anharmonic resonances. The complete database, made of 18,865 vibration-rotation lines accessing levels up to 10 120 cm(-1), is made available as Supporting Information.

The FT absorption spectrum of 13CH12CH: rotational analysis of the vibrational states from 3800 to 6750 cm−1

Thirty four cold bands and 37 hot bands are reported from the high resolution FT absorption spectrum of 13CH12CH, all leading to vibrational states located between 3800 and 6750u2009cm−1. Each band has been vibrationally assigned and rotationally analysed. The band centres and rotational constants are listed.

The vibrational energy pattern in acetylene VII: C12C13H2

In C12C13H2 129 vibrational term values up to 10000cm−1 are merged, about 60% of which are newly reported. They are fitted using an effective Hamiltonian with a standard deviation of 0.22cm−1. The vibrational assignments and vibrational constants are listed and discussed. The energy pattern is found to be very similar to the one in C212H2 with additional anharmonic resonances arising from the lack of u∕g character in the asymmetric isotopolog.

The FT absorption spectrum of (CH12CH)-C-13 (III): vibrational states in the range 6750 to 9500 cm(-1)

Forty cold bands and 29 hot bands are reported from the high resolution Fourier transform (FT) absorption spectrum of 13CH12CH, all leading to vibrational states located between 6750 and 9500 cm−1. Each of these bands has been vibrationally assigned and rotationally analysed. The band centres (ν c), vibrational term values (Gv ) and rotational constants are listed.

The FT absorption spectrum of 13CH12CH (II): rotational analysis of the range 9500 to 10000 cm−1

The infrared spectrum of 13CH12CH has been recorded in the 9500–10000u2009cm−1 wavenumber region by Fourier transform spectroscopy. Twelve Σ+–Σ+ and one ‘perturbation allowed’ Δ–Σ+ cold bands, and four Π–Π hot bands have been identified. All these bands have been rotationally analysed and vibrationally assigned. They mainly involve triple excitations of the CH stretching modes. The relative intensities have been measured. Local interaction patterns are identified and discussed. Line wavenumbers from the two strongest bands observed in the range are listed.

Erratum/ The bending vibrations in 12C2H2: Global vibration-rotation analysis (Molecular Physics (2007) 105:5 (559-568))

The author of this paper would like to change the following: The vibrational transition dipole moment of the 5– 4 FIR band determined to be 5 4 j j 1⁄4 0.55 D is incorrect. Indeed, it was found that the wavenumber ~ of the lines was overlooked in its determination from the measured line intensities. The correct value is 5 4 j j 1⁄4 0.051 D. It is comparable to that measured for C2D2, i.e. 0.0358 (20) D [1].