Mattia Villa

The stretching–bending bands of 13C2HD

The infrared spectrum of 13C2HD has been investigated using high-resolution Fourier transform infrared spectroscopy. A large number of ro-vibrational transitions in the spectral region 1000–6600 cm−1 have been recorded and assigned. This paper is focused only on the vibrational bands involving pure stretching, stretching–bending or stretching–stretching modes. In total, 78 bands have been identified and assigned, 29 related to υ1(CH stretch), 27 to υ2(CC stretch), and 22 to υ3(CD stretch). The data pertaining to each stretching mode have been fitted simultaneously in order to obtain accurate sets of rotational and vibrational parameters for the excited states.

The ro-vibrational analysis of the v4 fundamental band of CF3Br from jet-cooled diode laser and FTIR spectra in the 8.3-μm region

The v4 fundamental band of CF379Br and CF381Br, present in natural isotopic abundance, was investigated in the 8.3-μm region by high-resolution infrared spectroscopic techniques. Tuneable diode laser spectra were recorded in the ranges 1202.5–1205.0 cm−1, 1208.0–1210.1 cm−1 and 1212.5–1214.5 cm−1. The tuneable diode laser spectra were obtained at the reduced temperature of 200 K and in a free-jet expansion. The latter technique was used to reduce spectral congestion, achieving a rotational temperature of about 50 K, with a resolution up to 0.0008 cm−1. A Fourier transform infrared spectrum covering the entire spectral region of the v4 band, between 1190 and 1220 cm−1, was recorded at 298 K with a resolution of 0.004 cm−1. The experimental wavenumbers from the different spectroscopic techniques were combined to accomplish the complete ro-vibrational analysis of v4. In total, 4651 transitions were assigned to CF379Br, 4047 to CF381Br, with J″max  = K″max =80; of these, 3171 for CF379Br and 2755 for CF381Br are from diode laser measurements. The data of each isotopologue were analysed using the model Hamiltonian for a degenerate vibrational state of a molecule of C3v symmetry. The v4 band of both the isotopologues resulted essentially unperturbed, but the Δl = Δk = ±2 l-resonance was found to be active within the v4 = 1 state. Precise values of the vibrational energy and of the ro-vibrational parameters of v4 = 1 for CF379Br and CF381Br were obtained. The bromine isotopic splitting amounts to 6.9 × 10−3 cm−1. In addition, the equilibrium geometry and the harmonic force field were calculated ab initio using the large-size basis set def2-QZVP in conjunction to the PBE0 functional.

Femto-FT-CEAS investigation of rare acetylene isotopologues (H12C13CD, D12C13CH and D12C13CD)

The infrared spectrum of a sample containing 13C mono-substituted isotopologues of acetylene, H12C13CH, H12C13CD, D12C13CH and D12C13CD has been recorded in the 6130−6800 cm− 1 region using a femto-Fourier transform-cavity enhanced absorption spectroscopy (femto-FT-CEAS) apparatus. Three bands for both H12C13CD and D12C13CH were observed and analysed, namely 2ν1 − GS and associated hot bands from ν4 and ν5. The assignment of the 2ν1 overtone already reported in the literature [J.L. Hardwick, Z.T. Martin, M.J. Pilkenton, E.N. Wolf, J. Mol. Spectrosc. 243, 10 (2007)] was considerably extended to higher J values. For the D12C13CD isotopologue, four bands were analysed, ν1 + ν2 + ν3 − GS and associated hot bands from ν 4 and ν 5 and 2ν1 + ν4 + ν5 − GS.

The infrared spectrum of 12C2D2: The stretching-bending band system up to 5500 cm−1

The infrared spectrum of the perdeuterated acetylene, (12)C2D2, has been recorded from 900 cm(-1) to 5500 cm(-1) by Fourier transform spectroscopy at a resolution ranging between 0.004 and 0.009 cm(-1). Ninety-two bands involving the ν1, ν2, and ν3 stretching modes, also associated with the ν4 and ν5 bending vibrations and 9 bands involving pure bending transitions have been observed and analysed. In total, 8345 transitions for the stretching-bending, and 862 for the pure bending modes have been assigned in the investigated spectral region. All the transitions relative to each stretching mode, i.e. the fundamental, its first overtone, and associated hot and combination bands involving bending states up to v4 + v5 = 2, were fitted simultaneously. The Hamiltonian adopted for the analysis is that appropriate to a linear molecule and includes vibration and rotation l-type interactions. The Darling-Dennison interaction between v4 = 2 and v5 = 2 levels associated with the various stretching states was also considered. The standard deviation for each global fit is smaller than 0.0006 cm(-1), of the same order of magnitude of the measurement precision.

High-resolution FTIR spectroscopy of HCFC-31 in the 950−1160 cm−1 region: rovibrational analysis and resonances in the ν4, ν9 and ν5+ν6 bands of CH235ClF

The FTIR spectrum of CH2ClF (natural isotopic mixture) was investigated in the ν4, ν9 and ν5+ν6 band region between 950 and 1160 cm−1 at the resolution of 0.004 cm−1. The ν4 and ν5+ν6 vibrations of A′ symmetry give rise to a/b hybrid bands with a predominant a-type component. The ν9 vibration of A″ symmetry, expected with a c-type band contour, shows an intense Coriolis-induced parallel component (ΔKa = 0, ΔKc = 0) derived from mixing with the v4 = 1 vibrational state. The high-resolution spectra of ν9 and ν5+ν6 have been analyzed for the first time, while the assignments of the ν4 band, previously investigated, have been extended to higher J and Ka values in the b-type component. The spectral analysis resulted in the identification of 1508, 809 and 349 transitions for the ν4, ν9 and ν5+ν6 bands of CH235ClF, respectively. Besides the strong first-order a- and b-type Coriolis resonances between ν4 and ν9, the ν5+ν6 vibration was found to interact through a c-type Coriolis with the ν4 and 3ν6. High-order anharmonic resonance (ΔKa = ±2) between ν4 and ν5+ν6 was also established. All the assigned data were simultaneously fitted using the Watsons A-reduction Hamiltonian in the Ir representation and the relevant perturbation operators. The model employed includes five types of resonances within the tetrad ν4/ν9/ν5+ν6/3ν6. Α set of spectroscopic constants for ν4, ν9 and ν5+ν6 bands as well as parameters for the dark state 3ν6 and seven coupling terms have been determined. The simulations performed in different spectral regions satisfactorily reproduce the experimental data.

Accurate ro-vibrational rest frequencies of DC4H at infrared and millimetre wavelengths

Context. Diacetylene, C4H2, has been identified in several astronomical environments through its infrared spectrum. In contrast, monodeuterated diacetylene (DC4H) has not been detected in space so far owing to the low isotopic abundance of deuterated species but also to the rather poor laboratory spectroscopic characterisation of this molecule. Aims. The aim of this work is to provide accurate spectroscopic parameters for DC4H to achieve reliable predictions for both its spectra at millimetre and infrared wavelengths. Methods. We studied the rotational spectrum of DC4H in the range 85–615 GHz by millimetre-wave spectroscopy and the infrared spectrum below 1000 cm −1 by high-resolution, Fourier-transform spectroscopy. Several pure rotational transitions were recorded in the ground state and in excited vibrational bending states. The three fundamental bands v6, v7 ,a ndv8 have been identified and assigned in the infrared spectrum. Results. The rotational transitions were analysed together with the infrared data in a global fit that produces very accurate rovibrational parameters. The observed frequencies and wavenumbers are reported to provide precise guidance for astronomical searches.

High-resolution infrared spectroscopy of 13C12CD2: the bending states with υ4+υ5 up to 3

The high-resolution infrared spectrum of deuterated acetylene containing one 13C atom, 13C12CD2, has been recorded by Fourier transform spectroscopy in the range 450–1700 cm−1. The υ4 and υ5 bending fundamental bands and a number of overtone, combination and hot bands were identified. In total, 3210 rotation vibration transitions were assigned to 27 bands involving bending states with both υ4 + υ5 and |l4 + l5| up to 3. The ground state and 13 vibrationally excited states were characterised, i.e., all the l-vibrational components of the excited bending manifolds with υ4 + υ5 up to 2, (IIΠ), (IIΠ), and (Π and Φ). Two simultaneous least-squares fits of all assigned transitions have been performed, one considering transitions with υ4 + υ5 up to 2, the other adding the transitions with υ4 + υ5 = 3. The model Hamiltonian adopted for the analysis takes into account the usual vibration and rotation l-type resonances within each vibrational manifold and the Darling−Dennison anharmonic resonance between and , and between and . Two sets of 33 and 42, respectively, spectroscopic parameters were derived. They reproduce 1512 and 2450 assigned transitions with root mean square values of 3.5 × 10−4 and 3.9 × 10−4 cm−1, respectively. The transitions of four hot bands reaching the (IIΠ) state were fitted simultaneously to the effective upper state parameters.

The high-resolution infrared spectrum of DC4H from 450 to 1100 cm−1: Overtone, combination, and hot bands

The high-resolution infrared spectrum of monodeuterated diacetylene has been recorded in the 450-1100 cm(-1) spectral region by Fourier transform infrared spectroscopy. Seven new bands have been identified: the ν3 fundamental (C-C stretch), and the ν8 + ν9, ν7 + ν8, 2ν7, 2ν8, ν8 + ν9 - ν9, and ν6 + ν9 - ν9 combination, overtone, and hot bands. The assigned transitions, together with those previously reported for the fundamental bands [F. Tamassia, L. Bizzocchi, C. Degli Esposti, L. Dore, M. Di Lauro, L. Fusina, M. Villa, and E. Canè, Astron. Astrophys. 549, A38 (2013)], form a comprehensive data set which comprises more than 2500 ro-vibrational transitions, and involves all singly and most doubly excited vibrational states of DC4H lying below 1000 cm(-1). Rotational and vibrational l-type resonance effects among the sub-levels of excited bending states were considered in the analysis, which also included a careful treatment of the various anharmonic interactions coupling many vibrational states lying above 600 cm(-1). Reliable and unambiguous spectroscopic parameters were obtained for each investigated state, including the rotational and centrifugal distortion constants Bv and Dv, the l-type doubling parameter qt, the anharmonicity constants xL(89), xL(69), and the vibrational l-type terms r89, r69 for the v8 = v9 = 1 and v6 = v9 = 1 bend-bend combination states.

The spectroscopic analysis of the v2 = 1, v5 = 1, and v3 = v6 = 1 infrared vibration system of H3SiI

The ν2 (A1)/ν5 (E)/ν3+ν6 (E) band system of H3(28)SiI was investigated using Fourier transform infrared spectra recorded from 820 to 1100 cm(-1) at a resolution of 2.0×10(-3) cm(-1). In total, 11,903 transitions were assigned. Additional 1466 transitions reaching the v3=v6=1 state were obtained from the ν3+ν6-ν6 and ν3+ν6-ν3 hot bands near 360 and 590 cm(-1), respectively. Moreover, 30 highly accurate CO2 laser sideband transitions of the (r)Q0 branch of ν5 (J.M. Frye, W. Schupita, and G. Magerl, J. Mol. Spectrosc. 128, 427 (1988)) were implemented in the data set with J(max)″=140 and K(max)″=21. To adequately reproduce the complex pattern of interacting levels the Hamiltonian employed included 14 off-diagonal terms. These comprise x,y Coriolis ro-vibration resonances, between ν2/ν5, ν2/ν3+ν6 and ν5/ν3+ν6, and the anharmonic Fermi resonance between ν5/ν3+ν6. All these resonances strongly perturb the v2=1, v5=1, and v3=v6=1 excited states whose rounded deperturbed vibrational term values are 904.5, 941.1, and 953.7 cm(-1), respectively. In addition, the Δl=Δk=±2 l-resonance was found to be active within the v3=v6=1 state and between v5=1 and v3=v6=1; the Δl=±2,Δk=∓1 l-resonance within the v5=1 state and between v5=1 and v3=v6=1 was established, as well as the Δl=±1,Δk=∓2 α resonance between v2=1 and v5=1. A standard deviation of the fit, 0.48×10(-3) cm(-1), resulted which is ca. three times the estimated precision of experimental wavenumbers. Improved J-dependent ground state parameters of H3SiI were obtained by fitting 5420 combination differences, σ(fit)=0.22×10(-3) cm(-1).

The infrared spectrum of DCCF in the 320–850 cm−1 region: bending states up to υ4+υ5 = 3

Infrared spectra of deuterated monofluoroacetylene, DCCF, have been recorded in the region between 320 and 850 cm−1 at an effective resolution ranging from 0.0024 to 0.0031 cm−1. In total, 6650 rotation vibration transitions were assigned to 37 bands involving the bending states with v4 + v5 and |l4+l5|, respectively, up to 3, allowing the characterisation of the ground state and of 18 vibrationally excited states. The vν5 bending fundamental has been studied for the first time. In addition, the difference band v3 ← v4 has been detected and analysed. All the assigned transitions have been fitted simultaneously by adopting a model Hamiltonian that takes into account the vibration and rotation l−type resonances. Rotational transitions in the ground and in bending excited states reported in the literature have been included in the global analysis. The set of 57 derived spectroscopic parameters reproduces 6130 infrared and 90 microwave and millimetre−wave transitions satisfactorily with root mean square values of 5.3 × 10−4 cm−1 and 77 kHz, respectively.