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1.
The vibration-torsion-rotation spectrum of CH3SiH3 has been measured from 470 to 725 cm−1 at near-Doppler resolution. The full-width at half - maximum of the lines observed near 600 cm−1 was 0.0011 cm−1. The spectra were obtained using a Bruker IFS 125 HR Fourier transform spectrometer with the broadband source radiation being supplied from the synchrotron emission of the storage ring at the Canadian Light Source. Three vibrational bands were investigated: the lowest lying perpendicular fundamental ν12 centred near 524 cm−1, the lowest lying parallel fundamental ν5 near 703 cm−1, and the torsional hot band ν12 + ν6 − ν6 near 534 cm−1. For ν12 and ν5, the resolution and sensitivity are much improved over those in earlier studies, with many of the torsional multiplets now being resolved even in the cases where the upper levels are unperturbed. The primary motivation for the present work was the hot band, here reported for the first time, where the dependence of the silyl rock in ν12 on the torsional motion is much more pronounced. In addition, for the vibrational ground state (gs), two “forbidden” high torsional overtones v6 = 3 ← 0 and 5 ← 0 have been observed that become allowed through resonant mixing of the upper states with ν12 and ν5, respectively. In each case, two (Kσ) series have been measured where the mixing is largest. Here σ = 0, 1, −1 labels the torsional sub-levels. Using the Fourier transform waveguide spectrometer at E. T. H., the three σ-components of the (J = 1 ← 0) transition in ν12 + ν6 were observed, and a series of direct l-doubling transitions in ν12 + ν6 were measured for σ = 0. In a global fit, all the new data have been analysed along with the frequencies for other transitions obtained in earlier investigations. The analysis takes into account the relevant interactions among the torsional stacks of levels in the gs, ν12, and ν5. These include the previously known (gsν12) Coriolis-like and (gsν5) Fermi-like interactions along with a higher order (ν12ν5) Coriolis-like coupling introduced here. This last is responsible for the strong perturbation of the ν5 series with K = 10, 11, and 12, and of the corresponding hot band series. A good fit to 9282 frequencies including 7942 new measurements was obtained both with the Free Rotor model in which the torsion is classified as a rotation, and with the High Barrier model in which the torsion is classified as a vibration. The Hamiltonian is discussed with emphasis on the new terms required for treating ν12 + ν6 − ν6.  相似文献   

2.
The far infrared and infrared spectra of formamide (HCONH2) have been recorded at high resolution (0.00125 cm−1) in the region of 90-1060 cm−1. Over 20,000 transitions from the out-of-plane NH2 wagging motion (n12 = 1 ← 0 fundamental, n12 = 2 ← 0 overtone, n12 = 2 ← 1 difference bands), torsion (n11 = 1 ← 0 bands), and out-of-phase NCO/NH2 bend (n9 = 1 ← 0 bands) have been assigned. Molecular parameters have been obtained for the ground state and the unperturbed n12 = 1 state. The least-squares fit calculations were completed with the microwave data available in the literature. The complicated resonance system between the n12 = 2, n11 = 1, and n9 = 1 states has been investigated carefully. Thus, we have been able to verify almost all resonances (avoided crossing) existing in the region J, K investigated. In the coupled Hamiltonian used for the fit, all Watson’s reduced parameters, including the octic ones and 16 Coriolis coupling parameters were taken into account. The rms deviation obtained from the fit was 0.000247 cm−1.  相似文献   

3.
The ν9 fundamental band of ethane occurs in the 12 μm region. It is the strongest band of ethane in a terrestrial window and is commonly used for the identification of ethane in the Jovian planets. The ν9 + ν4 − ν4 band occurs in the same region; neither can be analysed as an isolated band, since both are embedded in the torsional bath of the ground vibrational state. We report here two global fit models including data from both of these bands as well as the ν3 fundamental and the ν4, 2ν4 − ν4, and 3ν4 torsional transitions. The first is restricted to −5 ? KΔK ? 15 in the hot band and gives an excellent fit to the included data. Three resonant interactions are identified in this fit—a Coriolis interaction with two resonant cases between the ν9 torsional stack and that of the ground vibrational state (gs) and a resonant Fermi interaction between the ν3 fundamental and the gs. Hot band lines with KΔK < −5 are influenced by a fourth perturbation, with a crossing at −11 < KΔK < −10, which has been attributed to an interaction with the ν12 fundamental. A second fit, demonstrating a promising treatment of this interaction, is also presented.  相似文献   

4.
The high-resolution spectrum of the ν1=5 stretching overtone of gaseous H70GeD3 has been recorded by an intracavity laser absorption spectrometer based on a vertical external cavity surface emitting laser (VECSEL). The rotational structure of the excited state at 9874.605 cm−1 was found weakly perturbed by unidentified interaction with dark states. Finally, of the 313 lines rotationally assigned, 239 lines were found unperturbed and could be reproduced with a root-mean-square (rms) deviation of 0.012 cm−1. The retrieved set of rotational parameters agrees with the values extrapolated from the previously studied ν1=6-8 stretching overtones. High-resolution FTIR spectra of the ν1 and 2ν1 bands have also been recorded and analyzed. The ν1=1 level, (νeff=2114.15 cm−1) is in anharmonic interaction with a further A1 symmetry level (νeff=2102.39 cm−1). The potential coupling term could be estimated (Wanh=5.6(3) cm−1) and the most probable assignment of the perturber is ν2+ν3. Moreover both levels are rotationally perturbed in an irregular fashion. Only a coarse analysis up to J=6 could be performed. The 2ν1 band reveals irregular perturbations of medium intensity by unknown dark states for almost all K values. Nevertheless the obtained leading rovibrational parameters of the 2ν1 band for J?6 are in agreement with those of the ν1=5-8 states.  相似文献   

5.
The infrared spectrum of the PD3 molecule has been measured in the region of the first stretching overtone bands on a Fourier transform spectrometer with a resolution of 0.0068 cm−1 and analyzed for the first time. More than 800 transitions with Jmax=15 have been assigned to the bands 2ν1 and ν1+ν3. An effective Hamiltonian was used which takes into account both the presence of resonance interactions between the states (2 0 0 0) and (1 0 1 0), and interactions of these with the third stretching vibrational state of the v=2 polyad, (0 0 2 0). A set of 44 spectroscopic parameters is obtained from the fit. This reproduces the 305 initial “experimental” upper rovibrational energies with an rms=0.0015 cm−1.  相似文献   

6.
The ν1(A1), Si-H stretching, ν2(A1) and ν4(E), Si-D stretchings, fundamental bands of HSiD3 have been recorded at an effective resolution of ca. 0.003 cm−1 between 2080 and 2280 cm−1 and between 1480 and 1720 cm−1, respectively. Ro-vibrational transitions of the H28SiD3 isotopologue have been assigned in the two spectral ranges, about 700 belonging to ν1, with J′ up to 25 and K up to 21, and about 1600 to the ν2/ν4 dyad, with J′ up to 24 and K′ up to 19. The spectra of all the bands evidence the existence of several perturbations. The transitions of ν1 have been analyzed either neglecting or including in the model A1/E Coriolis-type interactions with nearby dark states. The υ2 = 1 and υ4 = 1 states have been fitted simultaneously taking into account several ro-vibrational interactions between them and, in addition, with the υ5 = 2, l = 0 component, and with few other close dark states. The standard deviation of the fit for both ν1 and the ν2/ν4 dyad is, however, more than one order of magnitude larger than the estimated experimental precision and is independent on the adopted model.  相似文献   

7.
The high-resolution (0.0030 cm−1) Fourier transform infrared spectrum of CH279BrF has been studied in part of the atmospheric window between 910 and 980 cm−1, the region of the ν9 (935.847 cm−1) and ν5 + ν6 (961.239 cm−1) bands. The ν9 fundamental consists of a pseudo a-type band induced by Coriolis coupling with ν5 + ν6, in turn exhibiting a predominant a-type structure. Several interactions connecting these levels and the dark state 3ν6 have been assessed. The whole data set is treated using Watson’s A-reduced Hamiltonian in the Ir representation implemented with first order a- and b- and c-type Coriolis terms. A detailed analysis of the rotational structure yields a set of accurate upper-state parameters up to quartic distortion terms for ν9 and ν5 + ν6. In addition, spectroscopic information about the dark ternary overtone of ν6 has been obtained.  相似文献   

8.
The spectroscopic knowledge of sulfur hexafluoride, which is necessary for a correct remote sensing and monitoring of this species in the Earth’s atmosphere, is still very partial. In particular, the hot bands in the strongly absorbing ν3 region (near 948 cm−1) have not been analyzed yet. Their study implies the analysis of many vibrational levels and thus the spectroscopy of various fundamental, harmonic, and combination bands. The present work is a new contribution to this topic, concerning the ν2+ν4 combination band. The FTIR spectrum of this region has been recorded at room temperature with a resolution of 0.002 cm −1. The data have been analyzed thanks to the HTDS software (http://www.u-bourgogne.fr/LPUB/shTDS.html) developed in Dijon for XY6 octahedral molecules. Seven hundred and fifty-nine lines could be assigned up to J=112, and the standard deviation is 0.0022 cm−1. The distance between the two vibrational sublevels with respective symmetry F1u and F2u is 0.348 cm−1.  相似文献   

9.
The infrared spectrum of isotopically pure CH279BrCl has been recorded at a resolution of 0.0023 cm−1 (FWHM) in the range 550-800 cm−1 with a Bruker IFS 120 HR Fourier transform spectrometer in Wuppertal. Here we report the full rotational analysis of the ν4 and ν5 fundamentals and of the hot-bands ν4+ν6ν6 and ν5+ν6ν6. Ground state combination differences were constructed for all bands, yielding improved ground state constants, up to quartic terms, as well as reliable rotational constants for the ν4, ν5, and ν6 states.  相似文献   

10.
The ν18 fundamental band (∼158 cm−1) of acrolein is studied at high resolution (0.0015 cm−1) using synchrotron radiation from the Canadian Light Source facility and a Bruker IFS 125HR Fourier transform spectrometer. By fitting this band, together with some pure rotational transitions, molecular parameters are obtained to accurately determine the energies of the ν18 = 1 state levels for values of (JKa) up to at least (45, 24). These parameters should be useful for future high resolution studies of acrolein hot bands. This is demonstrated here by a detailed analysis of the (ν17 + ν18) − ν18 hot band at ∼589 cm−1. The upper state (ν17 + ν18) of this band is found to be perturbed by Coriolis interactions analogous to those affecting the ν17 state.  相似文献   

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