Hans Hollenstein

Dipole moment function and equilibrium structure of methane in an analytical, anharmonic nine‐dimensional potential surface related to experimental rotational constants and transition moments by quantum Monte Carlo calculations

The pure rotational spectrum in the far‐infrared and its absolute intensity in the vibrational ground state of CHD3 and CH3D, and the integrated band strength of the N=5 CH‐stretching overtone of CHD3 in the near infrared to visible were measured by high‐resolution interferometric Fourier transform techniques. The far‐infrared data result in permanent electric dipole moments (‖μz0‖=(5.69±0.14)×10−3 D for CHD3, ‖μz0‖=(5.57±0.10)×10−3 D for CH3D), consistent with previous experimental data. The integrated N=5 overtone cross section is found to be (0.828±0.068) fm2. The overtone data are used, together with previous data, to derive a new, nine‐dimensional, isotopically invariant dipole moment function for CH4 within the chromophore model for the CH chromophore in CHD3. With this function, the experimental data can be reproduced to an averaged factor of 1.2, in the best case. In the vibrational ground state, a nine‐dimensional calculation of expectation values on a new, fully anharmonic potential surface was ...

High resolution FTIR spectra of 12CF3I, 13CF3I and 12CF3 79Br near 1050 cm-1 and 550 cm-1

High resolution FTIR spectra of CF3 79Br, 12CF3I and 13CF3I have been studied and analysed in the region of the v 1 CF3 symmetric stretching fundamental which is accessible to CO2-laser pumping. Spectra with a resolution of 0.01 cm-1 have been obtained at various temperatures. J clusters were resolved and analysed by polynomial and simulation methods. In 13CF3I a Fermi resonance between v 1 (v eff = 1047.60 cm-1) and 4v 6 0 (v eff = 1049·51 cm-1) has been established. For CF3 35Cl, 12CF3 79Br and 12CF3I the Fermi resonance between v 1 and 2v 5 0 has been analysed semiquantitatively. Further rotational resonances occur in 12CF3I, which could not be assigned unambiguously, but are likely to be due in part to v 3 + 3v 6. The spectra of the v 5 fundamental near 550 cm-1 have been obtained for CF3Br and CF3I at a resolution of 0·05 cm-1. Whereas v 5 appears to be unperturbed for CF3 79Br, for CF3I a Fermi resonance between v 5 and v 3 + v 6 and a rotational resonance of v 5 with 2v 6 have been assigned. A set ...

High resolution infrared spectroscopy and global vibrational analysis for the CH3D and CHD3 isotopomers of methaney

We report infrared spectra of CH3D and CHD3 in the range 2900 to 9000 cm−1 measured with the Zürich high resolution Fourier transform infrared (FTIR) interferometer Bruker IFS 125 prototype (ZP 2001) at 80 K in a collisional-cooling cell with optical paths ranging from 5 to 10 m. In all, 57 new ro-vibrational bands of CH3D and 40 for CHD3 were assigned and analysed. Using a strategy of the direct assignment of the J = 0 states of excited vibrational levels, precise experimental values of the band centres with uncertainties in the range of about 0.0001 to 0.0003 cm−1 were obtained. Including 15 previously known band centres of CH3D and 12 previously known band centres of CHD3, these data were used as the initial information for the determination of the harmonic frequencies, anharmonic coefficients, and vibrational resonance interaction parameters in an effective hamiltonian. A joint set of 64 parameters reproduces the 124 experimental vibrational energies of both molecules up to 6500 cm−1 with a root mean deviation of d rms = 0.73 cm−1. The results are discussed in relation to intramolecular dynamics on a global potential hypersurface of methane, intramolecular vibrational redistribution, and the spectroscopy of the atmospheres of the earth and planetary systems.

High-resolution rovibrational analysis of vibrational states of A2 symmetry of the dideuterated methane CH2D2: the levels ν 5 and ν 7 + ν 9

The infrared spectrum of the CH2D2 molecule has been measured in the region 900–1500 cm−1 on a Bomem DA002 Fourier transform spectrometer with a resolution of 0.0024 cm−1 (FWHM, unapodized). Transitions belonging to the hot bands ν 7 + ν9−ν 7, ν7 + ν9− ν 9, ν5 + ν7−ν5, and ν5 + ν9−ν5 were extracted from the recorded spectra to determine the rovibrational energies of the A2 symmetry vibrational states (v 7 = v 9 = 1) at 2329.698 cm−1 and (v 5  = 1) at 1331.409 cm−1. Vibrational energies as well as rotational and centrifugal distortion parameters of the (v 7 = v 9=1) and (v 5 = 1) states were determined that reproduce the experimental rovibrational energy levels of the (v 7 = v 9 = 1) and (v 5 = 1) vibrational states with a d rms deviation of 0.0017 and 0.0006 cm−1, respectively. The results are discussed in relation to the equilibrium structure of methane, which is redetermined here from the experimental data, and in relation to its potential hypersurface and anharmonic vibrational dynamics.

High-resolution infrared spectrum and analysis of the v 11, A2u(B2) fundamental band of 12C6H6 and 13C12C5H6

High-resolution interferometric Fourier-transform infrared (instrumental bandwidth 0·0024 cm-1) and diode-laser (0·001 cm-1) spectra have been taken for the natural isotopic mixture of benzene in the range 640–710 cm-1. Accurate rotational-vibrational constants have been obtained for the fundamental v 11 (673·97465 cm-1) of 12C6H6 and for 13C12C5H6 = 673·6092 cm-1). Three hot bands have been analysed for 12C6H6 (v 11 + v 6 - v 6, 673·50873 cm-1; v 11 + v 16 - v 16, 672·87601 cm-1; and 2v 11 - v 11, 674·1021 cm-1). The results are discussed in relation to anharmonic and rotational-vibrational interaction constants and to force-field calculations. An analysis of available data for the ground-state rotational constant B 0 is presented, which shows rather large systematic discrepancies. All high-resolution results are consistent with B 0 = 5689·16 ± 0·3 MHz, where the absolute error estimate is 50 times the standard deviation from the present, most precise determination.

High resolution Fourier transform spectroscopy of CH2D2 in the region 2350–2650 cm−1: the bands ν5+ν7, 2ν9, ν3+ν4, ν3+ν7 and ν5+ν9

The IR spectrum of the CH2D2 molecule has been measured in the region of 2350–2650 cm−1 on a Bomem DA002 Fourier transform spectrometer with a resolution of 0.004 cm−1 (FWHM, apodized) and analyzed with a Hamiltonian model which takes into account resonance interactions between all vibrational states in that region. More than 3000 transitions have been assigned to the bands 2ν9, ν3 + ν4, ν5 + ν9, ν5 + ν7 and ν3 + ν7 using ground state combination differences from the known ground state parameters. A set of 115 spectroscopic parameters for the excited vibrational states is obtained from a least squares adjustment. This reproduces the 646 initial upper ro-vibrational energies used in the fit with a drms = 0.0036 cm−1.

Isotope effects in the fermi resonance of the CH chromophore in CHX3 molecules

Abstract High-resolution FTIR spectra have been recorded between 800 and 12000 cm−1 for 13CHCl3 and 13CHF3. Twenty bands for 13CHF3 and sixteen bands for 13CHCl3 could be assigned to CH chromophore absorption. A first theoretical analysis is given for the 13C isotope effect in the CHX3 Fermi resonance spectra of the CH chromophore and is discussed in relation to the CH chromophore potential and CD isotope effects.

The NH and ND stretching fundamentals of 14ND2H

High resolution (0.004 cm−1 instrumental bandwidth) interferometric Fourier transform infrared spectra of 14ND2H were obtained on a BOMEM DA002 spectrometer under essentially Doppler limited conditions. We report the analysis of the ND and NH stretching fundamentals of 14ND2H with term values for the symmetric (s) and antisymmetric (a) sublevels with respect to the inversion plane of the planar geometry Tv (s)=2430.7990(7) cm−1 and Tv (a)=2434.6222(8) cm−1 for the ν3a fundamental, Tv (s)=2559.8069(8) cm−1 and Tv (a)=2559.9630(9) cm−1 for the ν3b fundamental and Tv (s)=3404.238(5) cm−1 and Tv (a)=3404.316(5) cm−1 for the ν1 fundamental. The two modes ν3 which are degenerate in ND3 and whose degeneracy is lifted in ND2H, are distinguished by the subscripts 3a or 3b, being symmetric (3a) or antisymmetric (3b) with respect to the Cs plane of symmetry of the equilibrium geometry of ND2H. Up to 20 molecular parameters of the effective S-reduced Hamiltonian could be determined accurately for each fundamental. In...

Slit jet diode laser and FTIR spectroscopy of CF3I and improved analysis of the symmetric CF3 stretching chromophore absorption

Abstract We report measurements of the ν 1 fundamental absorption range of CF 3 I, involving several coupled vibrational levels. Both FTIR techniques (continuous jet, resolution up to 0.0024 cm −1 unapodized) and diode laser techniques (pulsed slit jet, resolution up to 0.001 cm −1 , achieving partial hyperfine resolution) were applied. We could newly establish a Coriolis resonance between ν 1 and ν 3 + 3ν +1 6 , and present spectroscopic parameters from an analysis involving explicitly six coupled vibrational levels. The results are discussed in relation to IR-multiphoton excitation of CF 3 I and to IR-MW double resonance experiments.

Analysis of the v4 and v1 bands of CF3Cl measured by supersonic free-jet ftir spectroscopy

The first successful detailed analysis of the high-resolution (0.005 cm−1) IR spectrum of the v4 band of CF3CI (