Filippo Tamassia

Absolute measurement of the S(0) and S(1) lines in the electric quadrupole fundamental band of D2 around 3 μm

The electric quadrupole fundamental (v=1←0) band of molecular deuterium around 3 μm is accessed by cavity ring-down spectroscopy using a difference-frequency-generation source linked to the Cs-clock primary standard via an optical frequency comb synthesizer. An absolute determination of the line position and strength is reported for the first two transitions (J=2←0 and J=3←1) of the S branch. An accuracy of 6×10(-8) is achieved for the line-center frequencies, which improves by a factor 20 previous experimental results [A. R. W. McKellar and T. Oka, Can. J. Phys. 56, 1315 (1978)]. The line strength values, measured with 1% accuracy, are used to retrieve the quadrupole moment matrix elements which are found in good agreement with previous theoretical calculations [A. Birnbaum and J. D. Poll, J. Atmos. Sci. 26, 943 (1969); J. L. Hunt, J. D. Poll, and L. Wolniewicz, Can. J. Phys. 62, 1719 (1984)].

The v3 band of 14C16O2 molecule measured by optical-frequency-comb-assisted cavity ring-down spectroscopy

The infrared spectrum of the rare isotopologue has been investigated in the range 2190–2250 cm−1 with a frequency-comb-referenced cavity ring-down spectrometer. Thirty-three ro-vibrational transitions of the ν3 fundamental band have been detected. Their absolute frequency was measured with a relative uncertainty ranging from to . The experimental frequencies were fitted to the conventional Hamiltonian of a linear molecule and a new set of spectroscopic parameters for the fundamental vibrational state has been improved for this species.

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 infrared spectrum of 12C2HD: the bending states up to υ4 +υ5 =3

The infrared spectrum of 12C2HD has been recorded at high resolution between 450 and 2100 cm−1 by Fourier transform spectroscopy. The ν4 and ν5 bending fundamental bands together with overtones, combination bands and associated hot bands involving modes up to υtot = υ4 + υ5 = 3 have been identified. Altogether, 43 vibrational bands have been analysed, leading to the spectroscopic characterization of the ground state and of 18 vibrationally excited states. They include all the components of the vibrational manifolds up to υtot = 3, with the exception of the υ4 = 3, ℓ = ±3 state. A simultaneous fit of all the assigned transitions has been performed. The adopted model includes vibration and rotation ℓ-type interaction resonances. The determined spectroscopic parameters reproduce the assigned wavenumber transitions with RMS values close to the estimated experimental uncertainties.

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 detection of the free radical FO (X 2Π3/2) by submillimeter-wave spectroscopy

Pure rotational transitions of the free radical FO in its X 2Π3/2 ground electronic state have been detected by millimeter-wave spectroscopy. Four transitions, which are all magnetic dipole in character, were measured in the frequency region from 219 to 408 GHz. The radical was produced by a well-known efficient reaction between ozone and fluorine atoms. The high sensitivity available in the submillimeter-wave region and a very efficient production method were essential for the detection of rotational transitions in this radical, which many other people have attempted in the past. No electric dipole transitions have been detected in this experiment. The precision of parameters associated with the rotational motion of FO has been improved considerably by fitting these lines together with previous data. Moreover, the parity-dependent nuclear spin rotation term CI′ has been determined for the first time. The r0 and re structures of FO have been revised accordingly.

Fine-structure spectrum of the FO radical, observed by far-infrared laser magnetic resonance

The fine-structure transition 2Π1/2←2Π3/2 of the free radical FO has been detected by far-infrared laser magnetic resonance. All the observed transitions are magnetic dipole in character. The spin–orbit constant A0 has been determined experimentally; its value of −196.108 686(50) cm−1 is consistent with previous estimates. The analysis of a set of 290 transitions leads to the determination of a number of molecular parameters including rotational, centrifugal distortion, spin–orbit, lambda-doubling, magnetic hyperfine, and Zeeman terms. All four magnetic hyperfine structure constants a, bF, c, d for the 19F nucleus have been determined and are discussed in terms of the expectation values of the appropriate operators over the electronic wave function.

The infrared spectrum of 13C2HD between 100 and 2100 cm−1: a global fit for the bending states up to υ 4 + υ 5 = 3

The fundamental bending ro-vibrational bands and a number of overtone, combination and hot bands of 13C2HD have been recorded by Fourier transform infrared spectroscopy in the range 450–2100 cm−1. In addition, the ν 5 ← ν 4 band, centred at 164.65 cm−1, has been identified in the spectrum of 13C2H2. The data were analysed simultaneously in a global fit that has provided very accurate rotational and vibrational parameters for the ground and vibrationally excited states.

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 accurate determination of magnetic hyperfine and Zeeman parameters for 2II diatomic molecules from experimental data

The parameters γ and AD (for the spin-rotation coupling and the centrifugal correction to the spin-orbit coupling) in the effective Hamiltonian of a diatomic molecule in a 2Λ state, Λ ≠ 0, make indistinguishable contributions to the energy, and one or other of these terms can be removed by a unitary transformation. The present work considers the effects of this and other transformations on the terms of the magnetic hyperfine and Zeeman Hamiltonians. It is found that the hyperfine parameter b is particularly affected by the transformations, and that care must be taken in correcting b before interpreting its value in terms of the electronic structure. An application to 15NO gives consistent values of the corrected b between ÃD and fits. The transformation of the Zeeman Hamiltonian produces higher order Zeeman terms that so far have not been included in fits of data in magnetic fields. Neglect of these contributions is equivalent to a constraint on the fit. A re-fit of LMR data for the FO radical shows that this approach is viable, and leads to the determination of separate values for AD and γ. These values and those obtained for b and gl correspond to the unitary transformation that optimizes the chosen form of the Zeeman Hamiltonian.