Studies in high resolution spectroscopy (original) (raw)
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Fourier-transform microwave and submillimeter-wave spectroscopy of chloroiodomethane, CH 2 ICl
Guided by a previous microwave study , the rotational spectrum of both chlorine isotopologues of chloroiodomethane in its vibrational and electronic ground state has been re-investigated in the microwave region and extended to the millimeter/submillimeter-wave region. Weak a-type transitions have been recorded by Fourier transform microwave spectroscopy below 20 GHz whilst strong btype rotational transitions have been recorded between 15 and 646 GHz, corresponding to energy levels with J 00 6 108 and K 00 a 6 12. Molecular constants including those describing the hyperfine structures owing to the two halogen atoms were accurately determined for both species from the least-squares analysis of a total of 1475 distinct transition frequencies (of which 906 belong to the CH 2 I 35 Cl isotopologue). The two sets of rotational constants allowed us to derive an r 0 structure of CH 2 ICl.
Journal of Molecular Spectroscopy, 2001
The high-resolution Fourier transform spectra of the DOCl molecule were recorded and analyzed in the region of the ν 1 and 2ν 2 bands. Transitions belonging to the ν 1 and 2ν 2 bands were assigned up to J max = 55 and 46, respectively. The sets of spectroscopic parameters of the (100) and (020) vibrational states obtained from the fit reproduce their energies derived from the experimental data with accuracies close to experimental uncertainties.
Journal of Molecular Structure, 2006
A broadband recording of the millimeter/submillimeter wave spectrum of formic acid heated to 170 °C with the FASSST spectrometer has yielded a multitude of rotational transitions of HCOOH in excited vibrational states. These include transitions of the cis-rotamer, the analysis of which is reported here. The data for the ground state could be significantly extended (546 lines), and the first information on rotational structure in vibrationally excited cis-HCOOH in the v9=1 and v7=1 states was obtained. Finally, transitions of cis-H 13COOH in the ground state were also observed. The rotational parameters resulting from the analysis of each of these spectra are reported, together with an initial determination of the Coriolis coupling parameters for the 7 1/9 1resonance interaction, an experimental force field calculation and a new structure determination.
The microwave spectrum, harmonic force field, and structure of formyl chloride
Journal of Molecular Spectroscopy, 1983
Extensive rn~u~rnen~ were made of the microwave spectra of nine isotopic species of formy1 chl&ie, HCOCl. Analysis of these spectra gave accurate rotational constants, chlorine nuclear quadrupole coupling constants, and cent&gal distortion constants. The distortion constants, to@her with the vibrational wavenumbers, were used to evaluate a valence harmonic force field. Effective, substitution, ground-state average, and estimated equilibrium structures are presented.
European Biophysics Journal, 1996
Theoretical infrared absorption spectra of aromatic ring molecules having up to 102 carbon atoms and with various edge hydrogenations have been obtained using a classic mechanical model and a simpliÐed valence force Ðeld. Force constants have been adapted from those available for smaller molecules. Spectral line intensities are calculated in a double harmonic approximation with e †ective atomic charges obtained using a tight-binding Hamiltonian. Vibrational modes of clusters of like aromatic ring Hu ckel molecules are obtained through introduction of an interlayer force constant. These modes are predicted to occur in the wavelength range between 80 and 400 km. We explore the e †ect of dehydrogenation on these spectra as well as hydrogenation of terminal C atoms in either aromatic or aliphatic form. Many spectra exhibit a quasi-continuum between 6 and 9 km that arises from the overlap of many vibrational modes in this region. With edge groups, we Ðnd a new spectral feature near 16 km and the ali-CH 2 phatic symmetric stretch vibration is found to shift from 3.5 to 3.3 km when these groups are CH 2 present at terminal sites on aromatic carbon skeletons. The relevance of calculated spectra to those of astronomical sources is brieÑy discussed.
The Journal of Chemical Physics, 2003
The fluorobenzene-hydrogen chloride -hydrogen-bonded complex has been studied by high resolution microwave spectroscopy and ab initio calculations. Rotational spectra of the C 6 H 5 F-H 35 Cl, C 6 H 5 F-H 37 Cl, and C 6 D 5 F-H 35 Cl isotopomers were assigned using pulsed molecular beam techniques in a Fourier-transform microwave spectrometer. The spectra are consistent with a structure of the complex in which the HCl is above the fluorobenzene ring near the ring center, similar to the benzene-HCl prototype dimer. An analysis of the inertial data and the chlorine quadrupole coupling tensor results in two mathematically possible locations for the HCl subunit with respect to the fluorobenzene arising from sign ambiguities in interpreting the spectral constants. One structure has the HCl nearly perpendicular to the aromatic ring; the other has the HCl pointing toward the fluorine end of the ring. Spectral intensities for the a and b transitions favor the former configuration. Ab initio calculations ͑MP2/6-311ϩϩG͑2df,2pd͒ϩBSSE corrections͒ indicate that the position of the HCl is driven by electrostatic interactions with the electrons of the benzene ring. HCl is shifted by 0.16 Å from the center of the ring toward the para-C atom, where the density is significantly higher. In the equilibrium form, HCl is tilted by ␦ϭ14°f rom perpendicular to the ring with the hydrogen end toward the para-C atom. The H atom can perform an internal rotation or at least a half-circular libration ͑barriers smaller than 100 cm Ϫ1 ͒.
The far-infrared and microwave spectra of the CH radical in the v=1 level of the X2Π state
Journal of Molecular Spectroscopy, 2008
Transitions between the spin-rotational levels of the 12 CH radical in the v = 1 level of the X 2 P state have been studied by the technique of laser magnetic resonance at far-infrared wavelengths. The data have been combined with a measurement of lambda-doubling transition frequencies at 7 GHz to determine an improved set of molecular parameters for CH in the v = 1 level. The parameters provide information on the effects of vibrational excitation on the structural properties of CH. Accurate predictions of the transition frequencies between the low-lying levels of the radical in the absence of a magnetic field have also been made. Small inconsistencies in the least-squares fit of the laser magnetic resonance data prompted re-measurement of three far-infrared laser frequencies, the 122.5 lm line of CH 2 F 2 pumped by 9R(22), the 122.5 lm line of CH 2 F 2 pumped by 9P(8) and the 554.4 lm line of CH 2 CF 2 pumped by 10P(14). The new measurements differ by as much as 3.8 MHz from those made previously and are more accurate; they also remove the inconsistencies in the fit. The re-measured frequencies of the two 122.5 lm lines are identical within experimental error which suggests that the far-infrared lasing transition is the same, namely the r R 23 (32) transition in the v 9 =1 level of CH 2 F 2 .
The ab initio RHF and MP2 force fields were calculated for chloramide with the use of the 6-3 I G>, 6-3 I G '* and 6-3 I IG '* basis sets. The ab initio force fields obtained were scaled by fitting to the available experimental vibrational frequencies for the H2NCI, H,N"CI and HDNCI species. This makes it possible to extend the set of transferable scale factors we recommended earlier. Minimal differences were observed between the scaled MP2 and RHF force fields, although the inclusion of electron correlation improved the ab initio data and showed better agreement with the observed frequencies obtained by scaling. The effect produced by empirical anharmonicity corrections to the observed NH(ND) stretching frequencies on the results of the fitting was tested. The experimentally observed satellite band at 1032 cm _' in rhe infrared spectrum of the parent substance was identified. and it was attributed to the presence of HNCI? in the sample, in contrast to previous assignments to vibrahons of H?NCI or any of its isotopomers. 0 1997 Elsevier Science B.V.
Journal of Molecular Spectroscopy, 2003
The microwave spectrum of o-chlorotoluene has been reinvestigated using molecular beam Fourier transform microwave (MB-FTMW) spectrometers in the frequency range of 4-23 GHz. Due to the high resolution of this molecular beam technique the analysis yielded improved rotational constants, centrifugal distortion constants, and, for the first time, the complete chlorine nuclear quadrupole coupling tensor. From the torsional fine structure the barrier to internal rotation of the methyl group was found to be 5.5798(52) kJ mol À1 . Experimental results and ab initio calculations are compared.