48 research outputs found
Measurement and calculation of CO (7-0) overtone line intensities
Intensities of 14 lines in the sixth overtone (7-0) band of carbon monoxide (12C16O) are measured in the visible range between 14 300 and 14 500 cm-1 using a frequency-stabilized cavity ring-down spectrometer. This is the first observation of such a high and weak overtone spectrum of the CO molecule. A theoretical model is constructed and tested based on the use of a high accuracy ab initio dipole moment curve and a semi-empirical potential energy curve. Accurate studies of high overtone transitions provide a challenge to both experiment and theory as the lines are very weak: below 2 à 10-29 cm molecule-1 at 296 K. Agreement between theory and experiment within the experimental uncertainty of a few percent is obtained. However, this agreement is only achieved after issues with the stability of the Davidson correction to the multi-reference configuration interaction calculations are addressed
Recommended Isolated-Line Profile for Representing High-Resolution Spectroscopic Transitions (IUPAC Technical Report)
The report of an IUPAC Task Group, formed in 2011 on Intensities and line shapes in high-resolution spectra of water isotopologues from experiment and theory (Project No. 2011-022-2-100), on line profiles of isolated high-resolution rotational-vibrational transitions perturbed by neutral gas-phase molecules is presented. The well-documented inadequacies of the Voigt profile (VP), used almost universally by databases and radiative-transfer codes, to represent pressure effects and Doppler broadening in isolated vibrational-rotational and pure rotational transitions of the water molecule have resulted in the development of a variety alternative line-profile models. These models capture more of the physics of the influence of pressure on line shapes but, in general, at the price of greater complexity. The Task Group recommends that the partially Correlated quadratic-Speed-Dependent Hard-Collision profile (pCqSD-HCP) should be adopted as the appropriate model for high-resolution spectroscopy. For simplicity this should be called the Hartmann-Tran profile (HTP). The HTP is sophisticated enough to capture the various collisional contributions to the isolated line shape, can be computed in a straightforward and rapid manner, and reduces to simpler profiles, including the Voigt profile, under certain simplifying assumptions. © 2014 IUPAC & De Gruyte
Recommended isolated-line profile for representing high-resolution spectroscopic transitions (IUPAC Technical Report)
The report of an IUPAC Task Group, formed in 2011 on "Intensities and line
shapes in high-resolution spectra of water isotopologues from experiment and
theory" (Project No. 2011-022-2-100), on line profiles of isolated
high-resolution rotational-vibrational transitions perturbed by neutral
gas-phase molecules is presented. The well-documented inadequacies of the Voigt
profile (VP), used almost universally by databases and radiative-transfer
codes, to represent pressure effects and Doppler broadening in isolated
vibrational-rotational and pure rotational transitions of the water molecule
have resulted in the development of a variety of alternative line-profile
models. These models capture more of the physics of the influence of pressure
on line shapes but, in general, at the price of greater complexity. The Task
Group recommends that the partially Correlated quadratic-Speed-Dependent
Hard-Collision profile should be adopted as the appropriate model for
high-resolution spectroscopy. For simplicity this should be called the
Hartmann--Tran profile (HTP). The HTP is sophisticated enough to capture the
various collisional contributions to the isolated line shape, can be computed
in a straightforward and rapid manner, and reduces to simpler profiles,
including the Voigt profile, under certain simplifying assumptions.Comment: Accepted for publication in Pure and Applied Chemistr
Observations of Dicke narrowing and speed dependence in air-broadened CO_2 lineshapes near 2.06 ÎŒm
Frequency-stabilized cavity ring-down spectroscopy was used to study CO_2 lineshapes in the (20013) â (00001) band centered near 2.06 ÎŒm. Two rovibrational transitions were chosen for this study to measure non-Voigt collisional effects for air-broadened lines over the pressure range of 7 kPaâ28 kPa. Lineshape analysis for both lines revealed evidence of simultaneous Dicke (collisional) narrowing and speed-dependent effects that would introduce biases exceeding 2% in the retrieved air-broadening parameters if not incorporated in the modeling of CO_2 lineshapes. Additionally, correlations between velocity- and phase/state changing collisions greatly reduced the observed Dicke narrowing effect. As a result, it was concluded that the most appropriate line profile for modeling CO_2 lineshapes near 2.06 ÎŒm was the correlated speed-dependent Nelkin-Ghatak profile, which includes all of the physical effects mentioned above and leads to a consistent set of line shape parameters that are linear with gas pressure
Absolute measurement of the ^{1}S_{0}âââ^{3}P_{0} clock transition in neutral ^{88}Sr over the 330 km-long stabilized fibre optic link
We report a stability below of two independent optical
lattice clocks operating with bosonic Sr isotope. The value
(429228066418008.3(1.9)(0.9)~Hz) of the absolute
frequency of the - transition was measured with an
optical frequency comb referenced to the local representation of the UTC by the
330 km-long stabilized fibre optical link. The result was verified by series of
measurements on two independent optical lattice clocks and agrees with
recommendation of Bureau International des Poids et Mesures
Subpromille Measurements and Calculations of CO (3â0) Overtone Line Intensities
Intensities of lines in the near-infrared second overtone band (3â0) of {12}^C{16}^O are measured and calculated to an unprecedented degree of precision and accuracy. Agreement between theory and experiment to better than 1â° is demonstrated by results from two laboratories involving two independent absorption- and dispersion-based cavity-enhanced techniques. Similarly, independent Fourier transform spectroscopy measurements of stronger lines in this band yield mutual agreement and consistency with theory at the 1â° level. This set of highly accurate intensities can provide an intrinsic reference for reducing biases in future measurements of spectroscopic peak areas