G. Di Lonardo

NH3 and PH3 Line Parameters: The 2000 HITRAN Update and New Results

This paper describes the improvements incorporated into the 2000 version of the HITRAN database for ammonia (NH_3), as well as newer results for phosphine (PH_3) not included in HITRAN 2000. For ammonia, the HITRAN 2000 database contains some 29084 ammonia lines, more than double the number of lines in HITRAN 1996. Specifically, the 2000 update involved replacing pure-rotational and infrared transitions from 0 to 3700 cm^(-1) with new calculations for the ^(14)NH_3 isotopomer, whereas in the 4000 to 5000 cm^(-1) region, parameters from the 1996 database were retained. The rotational quantum number range for line positions, intensities and line broadening parameters updated in this new HITRAN version goes up to J=22, 15, 13 and 10 in the 8–1000 μm, 5 μm, 4 μm and 2.8–3.3 μm spectral regions respectively. For phosphine, a new database from 770 to 2156 cm^(-1) available for future updates is described and contrasted with parameters in HITRAN 2000.

The ν2 and ν4 bands of AsH3

Abstract The infrared absorption of arsine, AsH3, between 750 and 1200 cm−1 has been recorded at a resolution of 0.006 cm−1. Altogether 2419 transitions, including nearly 700 “perturbation allowed” transitions with Δ∥k − l∥ = ±3, ±6, and ±9, have been assigned to the ν2(A1) and ν4(E) bands. Splitting of the transitions for K″ = 3, 6, and 9 was also observed. To fit the rotational pattern of the v2 = 1 and v4 = 1 vibrational states up to J = 21, all the experimental data were analyzed simultaneously on the basis of a rovibrational Hamiltonian which took into account the Coriolis interaction between ν2 and ν4 and also included several essential resonances within them. The derived set of 38 significant spectroscopic parameters reproduced the 2328 transition wavenumbers retained in the final fit within the accuracy of the experimental measurements.

The vibrational energy levels in acetylene. III. 12C2D2

We have performed the rovibrational analysis of the absorption spectrum of 12C2D2 between 5150 and 8000 cm−1, recorded by Fourier transform absorption spectroscopy, and between 12 800 and 16 600 cm−1, recorded by intracavity laser absorption spectroscopy. Respectively 10 and 9 bands are reported for the first time in each range. Improved or new rovibrational parameters were obtained for 34 vibrational levels altogether. The vibrational energies we obtained, together with those reported in the literature, were taken into account to model the vibrational energy pattern in 12C2D2(X 1Σg+). The analysis was performed in successive steps, inferring each time suitable parameters. The 44/55, 11/33, 12/33, and 1/244 quartic order anharmonic resonances were introduced during the procedure. They altogether define vibrational clusters which are characterized by only two dynamical constants of motion, Ns=V1+V2+V3 and k=l4+l5.

The vibrational energy pattern in acetylene. V. 13C2H2

A total of 134 vibrational levels with assigned rotational structure have been gathered in the ground electronic state of 13C2H2. Most of these measurements are updated or new compared to the previously published data. Altogether, they cover the range up to 23 670 cm−1. 118 out of the 119 levels observed below 13 000 cm−1 have been simultaneously fitted using the so-called cluster model, already used to deal with the vibrational energy levels in other isotopomers of acetylene [El Idrissi et al., J. Chem. Phys. 110, 2074 (1999), and references therein]. Twenty-nine vibrational constants have been determined, including the off-diagonal parameters K3/245, K1/244, K1/255, K11/33, K14/35, and r45, with a rms of the fit equal to 0.52 cm−1. The same three constants of the motion as in 12C2H2 emerged, Ns=v1+v2+v3, Nr=5v1+3v2+5v3+v4+v5 and k=l4+l5. The energies of the levels above 13 000 cm−1 calculated with the obtained parameters compare reasonably well with the experimental values. For all levels the predicted ...

Far infrared spectrum and spectroscopic constants of AsH3 in the ground state

Abstract The far ir spectrum of arsine, AsH 3 , was recorded in the range 25–100 cm −1 with a resolution of approximately 0.004 cm −1 . Δ J = +1, Δ K = 0 rotational transitions were measured and assigned up to J ″ = 12. These transitions, together with the presently available microwave and submillimeter-wave data and ground state combination differences, were analyzed on the basis of a rotational Hamiltonian which includes Δ k = ±3 and Δ k = ±6 interaction terms. The derived ground state molecular parameters reproduced the transition frequencies of both allowed and “perturbation allowed” transitions within the accuracy of the measurements. The equilibrium structure was determined for the AsH 3 molecule.

An intercomparison of laboratory measurements of absorption cross-sections and integrated absorption intensities for HCFC-22

Abstract An intercomparison of measurements of infra-red absorption cross-sections and integrated absorption intensities in HCFC-22 has been carried out. Independent measurements were made by five spectroscopy groups so that their experimental methods and data reduction techniques could be critically examined. The initial results showed a spread in reported values for integrated absorption intensity over the mid infra-red spectral region that were larger than the reported uncertainties. Re-examination of experimental and data reduction methods resulted in consistency of results within the reported errors. It was found that particular attention had to be paid to controlling and characterising errors associated with the non-linear response of MCT detectors and pre-amplifiers, adsorption of the sample on surfaces in the absorption cell, effectiveness of mixing when making measurements on mixtures of absorber gas and a buffer gas, and location of the photometric “full-scale” and “zero” levels.

The ν2, 2ν2, 3ν2, ν4, and ν2 + ν4 bands of 15NH3

The ir absorption of gaseous 15NH3 between 510 and 3040 cm−1 was recorded with a resolution of 0.06 cm−1. The ν2, 2ν2, 3ν2, ν4, and ν2 + ν4 bands were measured and analyzed on the basis of the vibration-rotation Hamiltonian developed by V. Spirko, J. M. R. Stone, and D. Papousek (J. Mol. Spectrosc. 60, 159–178 (1976)). A set of effective molecular parameters for the ν2 = 1, 2, 3 states was derived, which reproduced the transition frequencies within the accuracy of the experimental measurements. For ν4 and ν2 + ν4 bands the standard deviation of the calculated spectrum is about four times larger than the measurements accuracy: a similar result was found for ν4 in 14NH3 by S. Urban et al. (J. Mol. Spectrosc. 79, 455–495 (1980)). This result suggests that the present treatment takes into account only the most significant part of the rovibration interaction in the doubly degenerate vibrational states of ammonia.

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.

Empirical anharmonic force field and equilibrium structure of hypochlorous acid, HOCl

Abstract The cubic and quartic force fields of HOCl are investigated on the basis of the most recent experimental data on vibration-rotation interaction constants and anharmonicity constants. Some discrepancies with respect to previously reported ab initio results are found and discussed. The geometrical parameters of this molecule are also evaluated from recent data on the equilibrium values of the moments of inertia.