MAGNETIC CIRCULAR DICHROISM OF MATRIX-ISOLATED TANTALUM ATOMS

Author Institution:The magnetic circular dichroism and absorption spectra of Ta atoms isolated in an Ar matrix have been observed in the range 220 - 540 nm. Over sixty-five bands in the MCD spectrum were assigned by a comparison of signs and intensities of the $C_{o}$ terms with the J and gf values of the gas phase spectrum. An average shift to the blue of $786cm^{-1}$ (range: $573-976cm^{-1}$) was found for matrix spectrum. A g factor of $0.42\beta$ for the ground state of Ta in an Ar matrix was obtained from the temperature dependence of $C_{o}$ type band at 522.3 and 504.4 nm

Ab Initio Potential Energy Surface and Internal Torsional-Wagging States of Hydroxylamine

The two-dimensional potential energy surface describing the interaction of the large-amplitude torsional and wagging motions in hydroxylamine has been determined from ab initio calculations. This surface has been sampled by a large set of grid points from a two-dimensional configuration space spanned by the torsional and wagging coordinates. At each grid point, the geometry optimization has been performed using the second-order Møller-Plesset perturbation theory with the basis set 6-311 + G(2d, p). At the optimized geometry, the single-point calculation of the electronic energy has been carried out using a larger basis set 6-311 + G(3df, 2p). This method was verified to yield the results comparable to those obtained by a direct optimization of the geometry with the basis set 6-311 + G(3df, 2p) which had been used by A. Chung-Phillips and K. A. Jebber (1995. J. Chem. Phys. 102, 7080-7087) to calculate the energies of only three points in the potential energy surface of hydroxylamine. The trans and cis local minima have been found on the determined potential energy surface. The localization features of the torsional-wagging states have been studied by solving the two-dimensional Schrödinger equation for the coupled torsional and wagging motions. © 1997 Academic Press.The authors acknowledge financial support from the European Community in the form of a Human Capital and Mobility Network SCAMP (Contract CHRXCT93-0157 and its supplementary agreement CIPDCT94-0614).Peer Reviewe

Rotational spectrum and interstellar detection of the first torsionally excited state of methylamine

International audienceContext. Methylamine (CH 3 NH 2) was first detected in the interstellar medium (ISM) toward Sgr B2 almost 50 years ago by observation of rotational transitions in its torsional ground state. Methylamine exhibits two large-amplitude motions (LAMs), the methyl torsion and amine wagging, which complicate the spectral analysis, especially in excited vibration states. The lack of an accurate model of the two coupled LAMs has also hampered the identification in the ISM of rotational transitions in excited vibrational states. Aims. The aim of this work is to study the terahertz and microwave rotational spectra of methylamine experimentally and theoretically in order to provide a reliable basis for the detection of its rotational transitions in the first torsionally excited state, t = 1, in the ISM. Methods. The terahertz spectrum of methylamine was measured from 150 to 1520 GHz with the Lille fast scan spectrometer. Using a new "hybrid" Hamiltonian model, we were able to analyze the nuclear quadrupole hyperfine structure and to accurately fit the rotational spectrum of the t = 1 state of methylamine. We used the imaging spectral line survey ReMoCA performed with the Atacama Large Millimeter/submillimeter Array (ALMA) to search for rotational transitions of methylamine in its first torsionally excited state toward the high-mass star forming region Sgr B2(N). The observed spectra are modeled under the assumption of local thermodynamic equilibrium (LTE). Results. Accurate spectral predictions were obtained for the ground and first excited states of CH 3 NH 2. We report the first interstellar detection of methylamine in the t = 1 state toward the offset position Sgr B2(N1S) in the hot molecular core Sgr B2(N1). The LTE parameters derived previously from the rotational emission of methylamine in its torsional ground state toward Sgr B2(N1S) yield synthetic spectra of methylamine in the t = 1 state that are fully consistent with the ALMA spectra and allow us to identify five rotational lines of this state