A. Trombetti

Experimental and theoretical anharmonicity for benzene using density functional theory

The anharmonic force field of benzene has been calculated using a finite difference method by means of density functional theory (DFT) with the B3LYP functional and a TZ2P atomic orbitals basis set, and compared to the field calculated by Maslen et al. [J. Chem. Phys. 97, 4233 (1992)]. The vapor phase infrared (IR) spectra of benzene (natural isotopic mixture) and of 12C-benzene have been recorded from 450 to 6000 cm−1, at resolutions varying from 0.05 to 0.008 cm−1, and at various path lengths (0.18/42 m). The parallel bands ν11, ν4+ν12, ν5+ν12, ν2+ν11, and ν7+ν16, using the Wilson numbering, with their accompanying hot bands, have been analyzed and their origins determined to test our computed anharmonic force field. The Raman spectra of gas-phase benzene have been also recorded at medium resolution (∼0.7 cm−1) using an argon laser (line at 514.5 nm) with a power of 0.8 W and a multipass cell. In this work we compare the experimental and the theoretical frequencies and band profiles of the parallel ν1, ...

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.

The gas-phase infrared spectra of anthracene-h10 and anthracene-d10

The IR spectra of anthracene-h10 and -d10 have been recorded for the first time in the gas phase from 450 to 3200 cm−1 with a resolution of 0.2 cm−1, using a multipass cell heated to 100°C. For the assignment of vibrational bands we have evaluated the theoretical spectrum using density functional theory (DFT) and scaled self consistent field force fields. We found that both methods reproduce the sequence of the experimental frequencies to a good accuracy, allowing in most cases consistent and unambiguous assignments. The relative intensities of C14H10 and C14D10 have also been measured and compared to theory.

The Fourier spectrum of CH3OH: The region between 8 and 40 cm−1

Abstract The experimental Fourier spectrum of CH 3 OH has been investigated between 8 and 40 cm −1 . Good agreement was found between the experimental measurements and the results of the computational routines available up to now when low J values ( J ≲ 10) are involved. At higher J , the line assignments are possible by means of Taylor expansions of the energy levels. A catalog of almost 1500 lines, two-thirds of which have been assigned, is presented.

The far-infrared spectrum of hypochlorous acid, HOCl

Abstract Spectra of hypochlorous acid, HOCl, have been measured in the 30–210 cm −1 interval with a practical resolution of 0.002 cm −1 . The spectroscopic analysis led to the assignment of 868 ground state rotational transitions (up to J = 54 and K a = 6) for HO 35 Cl, and 775 transitions (up to J = 49 and K a = 6) for HO 37 Cl. Moreover, 327 pure rotational transitions (up to J = 5) within the v 3 = 1 vibrational state of HO 35 Cl were also assigned. Improved sets of molecular constants were obtained for the ground states of both isotopic species from the simultaneous analysis of our far-infrared measurements and the microwave and millimeter-wave data presently available. On the other hand, the parameters derived for the v 3 = 1 state are very similar to those reported in the literature.

Gas-phase infrared spectrum of indazole. Scaled quantum mechanical force field and complete spectrum assignment

The gas-phase IR spectrum of indazole has been recorded from 100 to 4000 cm–1, using a multipass cell heated to 120 °C, and completely assigned using theoretical predictions based on the scaled quantum mechanical (SQM) method. The single-crystal IR spectrum of this molecule, previously reported, has been compared with our data and partially reassigned. The harmonic force field of indazole, evaluated at the HF-SCF level using 6-31G** orbitals, is corrected by scaling the force field over a convenient set of internal coordinates. Scaling factors were determined by least-squares fitting of the theoretical to the experimental frequencies of two parent molecules, benzene and pyrazole and their perdeuteriated isotopomers. Our final prediction gives frequencies for indazole which, on average, differ from experiment by 24 cm–1. We confirm the validity of the SQM method as a practical tool for a complete analysis of vibrational spectra, even for molecules of this complexity.

The high-resolution spectrum of ozone between 8 and 150 cm−1

Abstract The rotational spectrum of 16 O 3 in the region 8–150 cm −1 has been measured at high resolution (0.0033 cm −1 at 30 cm −1 ) with a polarizing FT interferometer. From the rotational analysis of the present data (about 1000 transitions) combined with the previously reported millimeterwave data (about 210 transitions), a new set of rotational and centrifugal distortion constants was derived, which reproduces the measured transition frequencies within their accuracy.

The rotation-inversion spectrum of 15NH3

Abstract The rotation-inversion spectrum of 15 NH 3 has been recorded between 38 and 280 cm −1 with a resolution of about 0.03 cm −1 . By combining the present results with the inversion frequencies obtained by microwave spectroscopy, the following main rotational and centrifugal distortion constants were derived (in cm −1 ): State B D J D JK v inv = 0 9.92235 0.0008493 −0.001575 v inv = 1 9.91742 0.0008336 −0.001532

Gas-phase IR spectrum of 7-azaindole. Scaled quantum mechanical force field and complete spectrum assignment

The gas-phase IR spectrum of 7-azaindole has been recorded from 100 to 4000 cm–1, using a multipass cell heated to ca. 110 °C, and completely assigned using theoretical predictions based on the scaled quantum mechanical (SQM) method. The harmonic force field of 7-azaindole, evaluated at the HF-SCF level using 6-31G** orbitals, is corrected by scaling the force field over a convenient set of internal coordinates. Scaling factors were determined by least-squares fitting of the theoretical to the experimental frequencies of the two parent molecules, pyridine and pyrrole, and their perdeuteriated isotopomers. Our final prediction gives frequencies for 7-azaindole which on average differ from experiment by 18 cm–1.

Microwave spectrum and ab initio calculations of indazole

Abstract The microwave spectrum of indazole and its ND isotopomer has been investigated at 70°C. The tautomer with the NH group closer to the phenyl ring is found to be the more stable both by the analysis of the rotational spectrum and ab initio calculations. The second tautomer is calculated at HF/4–21G level of theory to be 2800 cm −1 higher in energy. Information on the dipole moment and the low energy vibrational excited states has also been obtained.