Perturbations in the infrared spectrum of monofluoroacetylene, and their relationship to intramolecular vibrational energy redistribution

Several high-order vibration-rotation perturbations in the high-resolution infrared spectrum of monofluoroacetylene, HCCF, are assigned and analyzed in detail. They result in avoided crossings in the rotational structure of several bands, and precise values for the effective high-order terms in the Hamiltonian have been determined. The significance of these results for intramolecular vibrational redistribution is discussed.

Enhanced signature of solar variability in Eurasian winter climate

We demonstrate that a new geomagnetic index of solar variability exhibits stronger correlations with atmospheric circulation variations than conventional measures. The circulation anomalies are particularly enhanced over the North Atlantic / Eurasian sector, where there are large changes in the occurrence of blocking and the winter mean surface temperature differs by several degrees between high- and low-solar terciles. The relationship is also simpler, being largely linear between high- and low-solar winters. While the circulation anomalies strongly resemble the North Atlantic Oscillation they also extend deeper into Eurasia, in a distinct signature which may be useful for the detection and attribution of observed changes and also the identification of dynamical mechanisms.

Solar influences on climate

Understanding the influence of solar variability on the Earth’s climate requires knowledge of solar variability, solar-terrestrial interactions and the mechanisms determining the response of the Earth’s climate system. We provide a summary of our current understanding in each of these three areas. Observations and mechanisms for the Sun's variability are described, including solar irradiance variations on both decadal and centennial timescales and their relation to galactic cosmic rays. Corresponding observations of variations of the Earth’s climate on associated timescales are described, including variations in ozone, temperatures, winds, clouds, precipitation and regional modes of variability such as the monsoons and the North Atlantic Oscillation. A discussion of the available solar and climate proxies is provided. Mechanisms proposed to explain these climate observations are described, including the effects of variations in solar irradiance and of charged particles. Finally, the contribution of solar variations to recent observations of global climate change are discussed.

The fundamental vibration-rotation band of hydrogen chloride

The fundamental vibration-rotational absorption band of hydrogen chloride near 3 45,t has been remeasured using higher resolving power than previously. The wave-lengths of the absorption lines have been determined more precisely, and the isotopic splitting of lines has been completely resolved. The results have provided new and more satisfactory values for the rotational constants Bi, and the centrifugal stretching constants Di, and their relative values for the two isotopic species agree closely with what is to be expected for the difference in mass. The positions of the lines in the pure rotational absorption spectrum have been calculated from the derived data, and agree closely with those recently observed. The bond lengths re for each isotopic species H35C1 and H37C1 is found to be 1-2744A.

Internal rotation in dimethylacetylene

The vibrational spectrum of dimethyl acetylene has been remeasured with better resolving power than hitherto, and the rotational fine structure of some perpendicular type bands has been partly analyzed. The energy levels of a molecule of this kind in which internal rotation of methyl groups may arise have been re-examined theoretically and the rotational structure of the absorption bands has been more clearly defined than previously. The experimental results are consistent with the assumption of unrestricted internal rotation of the methyl groups, and the Coriolis factors $\zeta _{i}$ for several vibrations have been determined.

Microwave spectrum of CF3CCH

Attempts to observe ΔK = ±1 transitions in the rotational spectrum of CF3CCH and CF3H in the first excited state of a degenerate vibration, by direct absorption in the Y band and K band regions of the microwave spectrum, have not been successful. In the course of this work the J = 3-2 and 4-3 rotational spectrum of CF3CCH has been observed with higher sensitivity than previously, and from the positions of the vibrational satellites several new rB values have been determined.

Puckering structure in the infrared spectrum of cyclobutane

The theory of rotational-pucker-vibrational transitions in the vibrational spectrum of cyclobutane is reviewed. Puckering sideband structure on the 1453 cm-1v14 infra-red fundamental of C4H8 has been observed and analysed, in terms of two slightly different puckering potential functions for the ground and the excited vibrational states. The results have been fitted to quartic-quadratic potential functions in the puckering coordinate, with a barrier to inversion of 503 cm-1 (1•44 kcal mole-1 = 6•02 kJ mole-1) in the ground state and 491 cm-1 in the excited state ν14 = 1. For reasonable assumptions about the reduced mass, the equilibrium dihedral angle of the C4 ring is determined to be about 35°, in agreement with previous estimates. Ueda and Shimanouchi's observations on the 2878 cm-1 C4H8 band have been re-analysed, and puckering sidebands have also been observed and analysed for the 1083 cm-1v14 infra-red fundamental of C4D8. Pure puckering transitions have been observed in the Raman spectrum of C4H8 vapour. All of these observations are shown to be consistent with the same ground state puckering potential function.

Infrared and Raman selection rules for cyclopentane

Infra-red and Raman selection rules are obtained for the cyclopentane molecule, on the assumption that it has a free pseudo-rotation with a large potential hump at the D5h configuration. The selection rules obtained, which concern the vibrational, pseudo-rotational, and rotational quantum numbers, are summarized in tables 1, 2 and 3.

Overtone bandshapes and IVR: CH stretch overtones in CHCl3

The intracavity photoacoustic dye laser spectrum of CHCl3 in the gas phase at 16 350 cm−1 is reported. The v=6–0 overtone of the CH stretch is observed, and found to exhibit a rotational band contour closely analogous to the v=1–0 fundamental. The implication of this result for intramolecular vibrational energy redistribution is discussed.

Carbon suboxide: the vibrational dependence of the v7 bending potential function

Data on the vibrational energy levels and rotational constants of carbon suboxide for the low-wavenumber bending mode ν7 are reviewed, in the ground-state manifold, and in the ν2-, ν3-, ν4-, and ν2 + ν4-state manifolds. Following the procedure developed by Duckett, Mills, and Robiette [J. Mol. Spectrosc. 63, 249 (1976)] the data have been inverted to give the effective bending potential in ν7 for each of these five states. Values are obtained for various other parameters in the effective vibration-rotation Hamiltonian. The potential and rotational constants in ν2 + ν4 are given to a close approximation by linear extrapolation from the ground state through the ν2 and ν4 states.

The microwave spectrum of 1-pyrazoline

The microwave spectrum of 1-pyrazoline has been observed from 18 to 40 GHz in the six lowest states of the ring-puckering vibration. It is an a-type spectrum of a near oblate asymmetric top. Each vibrational state has been fitted to a separate effective Hamiltonian, and the vibrational dependence of both the rotational constants and the quartic centrifugal distortion constants has been observed and analyzed. The v = 0 and 1 states have also been analyzed using a coupled Hamiltonian; this gives consistent results, with an improved fit to the high J data. The preferred choice of Durig et al. [J. Chem. Phys. 52, 6096 (1970)] for the ring-puckering potential is confirmed as essentially correct, but the A and B inertial axes are shown to be interchanged from those assumed by Durig et al. in their analysis of the mid-infrared spectrum.

Microwave spectrum of deuterated silyl isocyanate, SiD3NCO

The microwave spectrum of SiD3NCO has been observed and analyzed for 18 different vibrational states in the ν10 manifold. Some accidental resonances have been observed and analyzed. The vibrational dependence of the rotational and l-doubling constant and centrifugal distortion constant DJK has been successfully interpreted in terms of the two-dimensional anharmonic oscillator model.

The high-resolution infrared spectrum of HOF near 2700 cm-1: the ground and 2v2 states

The a/b hybrid-type ν1 fundamental and 2ν2 overtone bands of HOF were investigated by FTIR spectroscopy with a resolution close to 0.008 cm−1. Improved ground state parameters of HOF were determined from a merge of more than 3000 ground state combination differences formed from ν1 and previously measured ν2 transitions with the reported pure rotational lines. Excited state parameters of the v2 = 2 state, ν0 = 2686.924 6(1) and χ22 = −9.942 4(1) cm−1, were determined employing Watson's A-reduced Hamiltonian up to sixth order in I′ representation. The 2ν2 state was found to be unperturbed, the excited state parameters being closely related to those of ν2.

The calculation of force constants and normal co-ordinates--VII Normal co-ordinates in the E species of allene

Force constant and normal co-ordinate calculations are reported for the E species vibrations of the allene molecule. Data on the fundamental vibration frequencies of allene-h4, allene-d4 and allene-1.1-d2 and on the five experimentally determined Coriolis zeta constants of C3H4 and C3D4, were used in a force constant refinement procedure. Allowing for product and sum rules this gives 21 independent data which were used to refine to the most general harmonic force field (10 parameters) with one constraint (in the absence of any constraints the refinement was not satisfactory). The results have been used to calculate the complete ζz Coriolis interaction matrix for the allene-1.1-d2 molecule, and hence to calculate the expected rotational structure of the perpendicular bending vibrations of this molecule; the good agreement obtained with the observed spectra is a check on our results.

The fundamental vibration-rotation bands of 13C16O and 12C18O

Rotation lines in the fundamental vibration bands of 13C16O and 12C180 have been measured, using very high resolving power and more accurate wavelength calibrations than previously. The molecular rotational and vibrational constants have been deduced and compared in relation to the mass differences between these molecules and the main species 12C160.