Andreas Amrein

Multiple anharmonic resonances in the vibrational overtone spectra of CHClF2

The vibrational spectra of chlorodifluoromethane (Freon 22) have been measured at intermediate and high resolutions between 800 and 12 000 cm-1 by interferometric (FTIR) techniques. The CH overtone spectra exhibit a pronounced multiple-resonance structure which can be understood in terms of the ‘universal’ anharmonic CH stretching-bending hamiltonian. Quantitative predictions from this hamiltonian agree well (without adjustments) with previous experimental data on the visible spectra, which could not be correctly assigned before.

Group additivity and overtone intensities for the isolated CH chromophore

Abstract Integrated band strengths for CH fundamental and overtone transitions (up to N = 4) are reported for the isolated CH chromophore in six compounds C n F m Cl k H. The experimental (vapour) data are analyzed by means of one-dimensional anharmonic oscillator transition moments for the Mecke dipole moment function μ( r ) ∝ r m c −α r . The recently established triagonal Fermi resonance of the CH chromophore is taken into account in the analysis.

High-resolution FTIR spectroscopy of CHClF2 in a supersonic free jet expansion

Abstract The infrared spectrum of CHClF 2 (freon 22, chlorodifluoromethane) in the range of the CH stretching fundamental ν 1 and the two CF stretching fundamentals ν 3 and ν 8 has been measured in a supersonic free jet expansion with rotational temperatures of about 50 K and resolutions up to 0.004 cm −1 . The first successful rotational analyses for CH 35 ClF 2 provided band centers and other constants for ν 3 (1108.728 cm −1 ), for ν 8 (1127.284 cm −1 ), and for the ground state by combination differences. The peculiar double-peak structure of ν 1 (3021.6 cm −1 with a side maximum near 3024.6 cm −1 ) is discussed. The results are also important for a better understanding of the IR laser chemistry of CHClF 2 and simulations of its IR absorption as an atmospheric trace gas.

High resolution interferometric Fourier transform infrared absorption spectroscopy in a supersonic free jet expansion

The absorption spectrum of CHF3 in a free jet expansion has been recorded at a resolution of 0·004 cm-1 in the 8–9 μm region. The line width is found to be essentially Doppler limited. An approximate rotational temperature of 40K has been determined from the spectrum. Relative intensities and transition moments for the interacting bands are discussed.

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 (

High resolution interferometric fourier transform infrared spectroscopy in supersonic free jet expansions: N2O, CBrF3 and CF3I

v0= 1216.75843(20) cm−1 for 35Cl) is reported on the basis of a measurement in a supersonic free jet. The rotational and vibrational cooling in the jet is evaluated from the spectra of v1 and v4 and their hot bands. Rotational temperatures are 32 ± 7 K and vibrational temperatures of the hot band (v1+v6)-v6 about 240 ±30 K. The results are important in relation to IR laser chemistry and to modelling the absorption of freons in the atmospheric window.

The rotational structure of the v 4-band of CH35ClF2

Continuous flow supersonic jet expansions of neat nitrous oxide N2O, bromotrifluoro methane CBrF3 and trifluoroiodo methane CF3I have been investigated by FTIR absorption spectroscopy in the 8–9 μm region at high resolutions of 0.004 and 0.0024 cm−1 (fwhm). Rotational temperatures of 26 K for N2O, 45 K for CBrF3 and 50 K for CF3I have been determined from the spectra. For the v1 band of N2O the contribution of background gas to the FTIR spectrum and to the nonlinearity of Boltzmann plots has been evaluated. New spectroscopic parameters have been determined for the v1 and v1 + v6 − v6 bands of C79BrF3 and C81BrF3 with band centers v−01 (C79BrF3) = 1084.7690(1),~ v01 (C81 BrF3) = 1084.5214(1), ~v0166(C79BrF3) = 1083.5292(2) and ~v0166 (C81BrF3) = 1083.2846(2) cm−1 as well as for the v4 band of 12CF3I with band center ~v04 = 1187.6275(1) cm−1. The results are important for IR-multiphoton excitation, laser chemistry, and atmospheric chemistry and spectroscopy.

Free-jet high-resolution FTIR spectroscopy of the complex structure of the ν1 band of CF3I near 9 μm

FTIR spectra have been taken in the v 4 fundamental absorption range (Fermi resonance with 2v 6) with an experimental bandwidth of about 0·005cm-1 both at room temperature and in a supersonic jet with a rotational temperature of about 50K. The v 4 band was fully analysed giving an accurate effective band centre for v 4 (CH35ClF2) of 809·2726 cm-1. The following band centres could be estimated from the jet spectrum: v 4(CH37ClF2) = 804·502cm-1, 2v 6(CH35ClF2) = 829·062cm-1, 2v 6(CH37ClF2) = 820·900cm-1.

High-resolution interferometric Fourier transform infrared absorption spectroscopy in supersonic free jet expansions: carbon monoxide, nitric oxide, methane, ethyne, propyne, and trifluoromethane

Abstract The ν1 band of trifluoromethyl iodide (CF3I) has been investigated by high-resolution (0.005 cm−1) FTIR spectroscopy of a supersonic free jet at a rotational temperature of 45±15 K. Narrow J-resolved Q(P, R)(J) clusters were found for 2ν50 ( ν 0=1080.1502(9) cm−1), with considerable intensity due to anharmonic interaction with ν1. The Q branch of ν1 ( ν 0=1075.658(4) cm−1) is split by anharmonic resonance with ν3+3ν6−3 ( ν 0=1073.758(15) cm−1, W3666=0.5367(8) cm−1), a level crossing occurring near K=8. The K⩾12 levels of ν1, associated with QQ branches at lower wavenumbers, appear to be, in addition, rotationally perturbed. Several of the previously observed coincidences with CO2 laser lines are perfectly matched by the proposed model, and apparent inconsistencies explained. The implications for IR multiphoton excitation are discussed.