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Structure and rovibrational analysis of the [O2(1Δg)v=0]2←[O2(3Σg−)v=0]2 transition of the O2 dimer (2000)

Biennier, Ludovic ; Romanini, Daniele ; Kachanov, Alexander ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 112 (2000), S. 6309-6321

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The rotationally resolved absorption spectrum of the O2 dimer involving the [O2(1Δg)v=0]2←[O2(3Σg−)v=0]2 transition has been recorded near 632.6 nm by continuous wave Cavity Ring Down Spectroscopy in a supersonic slit jet expansion of pure O2. A quadratic dependence of the absorption in the jet versus the stagnation pressure is observed. A rotational temperature of 12 K is derived from the (O2)2 rotational analysis. The high spectral resolution of the CW-CRDS measurements limited by the residual Doppler broadening in the jet and the low rotational temperature allow the first rotational analysis in this open-shell complex. The same spectrum was also recorded by Intracavity Laser Absorption Spectroscopy and the comparison of the performances of the two methods is discussed. Among more than 600 lines measured between 15 800 and 15 860 cm−1 from the CW-CRDS spectrum, 40 were assigned to the RP0, RQ0, and RR0 branches of two subbands associated with B1−←A1+ and A1+←B1− transitions between the ground and excited rovibrational levels, labeled following the G16 permutation inversion representation. Forty five lines were assigned to PP2, PQ2, and PR2 branches of two subbands associated with B1−←A1+ and A1+←B1− transitions. The subbands centered at 15 808.401(49) [A1+←B1−] and 15 813.134(37) cm−1 [B1−←A1+] for those arising from K=0, and at 15 812.656(20) [A1+←B1−] and 15 818.277(35) [B1−←A1+] when arising from K=2, are analyzed considering (O2)2 as a slightly asymmetric prolate top. The rotational analysis of the two K=0 subbands leads to very close values of the effective rotational constant, Bp=(B+C)/2, for both A1+ and B1− levels: 0.095 cm−1 for the [O2(3Σg−)v=0]2 lower states and 0.063 cm−1 for the [O2(1Δg)v=0]2 excited states, in close agreement with theoretical values. The H geometry is confirmed as the most stable for the ground electronic singlet state. A distance between the two monomers of 6.1 a0 and 7.5 a0 is derived for the ground and excited singlet states. Similar results are obtained from the two K=2 subbands. A vibrational assignment is given for the two rotationally analyzed subbands (K=0) and proposed for the main features of the whole band. © 2000 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.481192

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Cavity ring-down overtone spectroscopy of HCN, H13CN and HC15N (1995)

Romanini, Daniele ; Lehmann, Kevin K.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 102 (1995), S. 633-642

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: This paper reports the results of our use of Cavity Ring Down Spectroscopy to extend the study of highly excited vibrational states in HCN. We extend our previous study of the H12C14N isotopomer, reporting on some weaker bands between 17 500 and 19 500 cm−1. We also report spectra of overtone and combination bands with six, seven, and eight quanta of stretching vibration in the isotopomers H12C15N and H13C14N in the interval from 17 500 to 23 000 cm−1. The observed spectroscopic constants and band intensities are compared with calculated values. All but one of the observed bands can be fit to within experimental accuracy (∼0.02 cm−1) to the standard distortable–rotor Hamiltonian. The one perturbed band has been successfully analyzed in terms of three anharmonically coupled levels. An anomalous line intensity distribution has been observed in the 1115 and 0116 Π←Σ bands, which we believe is produced by Coriolis coupling. © 1995 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.469462

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Calculation of the Herman–Wallis effect in Π–Σ vibrational overtone transitions in a linear molecule: Comparison with HCN experimental results (1996)

Romanini, Daniele ; Lehmann, Kevin K.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 105 (1996), S. 68-80

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The high sensitivity of cavity ring-down spectroscopy has allowed us to observe a few perpendicular vibrational overtone transitions of HCN in the visible. These transitions display a sizable Herman–Wallis effect, that is an asymmetry in the relative intensities of the R and P branch lines. We have developed a theory for the first-order Herman–Wallis effect based upon using variational vibrational wave functions but treating the vibration–rotation interaction by first-order perturbation theory. In the specific case of perpendicular transitions, the first-order effect is dominated by Coriolis mixing of Σ and Π overtone states. We used the empirical energy surface by Carter, Mills, and Handy [J. Chem. Phys. 99, 4379 (1993)] restricted to the stretching degrees of freedom. Bending was included by multiplication of these stretching wave functions by harmonic wave functions of the bend. Vibrational transition moments were calculated using a polynomial surface fit to ab initio CCSD(T) dipole moment points by Botschwina et al. [Chem. Phys. 190, 345 (1995) and private communication]. We expected that this treatment would be accurate but the calculated Herman–Wallis effect is about one order of magnitude too large. To gain further insight into the poor agreement between theory and experiment, we have calculated the sensitivity of the Herman–Wallis coefficient and of the transition moment to the dipole and energy surface parameters. From this, it appears that the dipole surface, while producing accurate band intensities, could at the same time be inadequate to account for the Herman–Wallis effect. A similar possibility stands for the energy surface, which however is highly constrained by the requirement to fit the observed band origins. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.471882

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4

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The superposition principle and cavity ring-down spectroscopy (1996)

Lehmann, Kevin K. ; Romanini, Daniele

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 105 (1996), S. 10263-10277

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Cavity ring-down is becoming a widely used technique in gas phase spectroscopy. It holds promise for further important extensions, which will lead to even more frequent use. However, we have found widespread confusion in the literature about the nature of coherence effects, especially when the optical cavity constituting the ring-down cell is excited with a short coherence length laser source. In this paper we use the superposition principle of optics to present a general and natural framework for describing the excitation of a ring-down cavity regardless of the relative values of the cavity ring-down time, the input pulse coherence time, or the dephasing time of absorption species inside the cavity. This analysis demonstrates that even in the impulsive limit the radiation inside a high finesse cavity can have frequency components only at the natural resonance frequencies of the cavity modes. As an immediate consequence, a sample absorption line can be detected only if it overlaps at least one of the cavity resonances. Since this point is of particular importance for high resolution applications of the technique, we have derived the same conclusion also in the time domain representation. Finally, we have predicted that it is possible to use this effect to do spectroscopy with a resolution much higher than that of the bandwidth of the excitation laser. In order to aid in the design of such experiments, expressions are derived for the temporal and spatial overlap of a Fourier transform limited input Gaussian beam with the TEMmn modes of the cavity. The expressions we derive for the spatial mode overlap coefficients are of general interest in applications where accurate mode matching to an optical cavity is required. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.472955

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5

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Line-mixing in the 106←000 overtone transition of HCN (1996)

Romanini, Daniele ; Lehmann, Kevin K.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 105 (1996), S. 81-88

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: By using cavity ring-down spectroscopy (CRDS), we have obtained visible overtone absorption spectra of HCN which display a large collisional line-mixing effect in the proximity of the R branch band heads, for J∼18. We consider in detail the 106←000 (1=CN, 0=bend, 6=CH) parallel transition. The R branch profile was modeled using the modified-exponential-gap (MEG) and energy-corrected-sudden approximation (ECS) population transfer rate laws. We used the rates previously determined by Pine and Looney (PL) by fitting the self broadening coefficients measured for the Q branches of Π–Σ infrared perpendicular stretch–bend combination bands of HCN [J. Chem. Phys. 96, 1704 (1992)]. Contrary to what is found by these authors, in the present case the MEG law reproduces the R branch line-mixing satisfactorily, while the ECS model fails. This reflects an increasing propensity at higher J for collisional transitions with smaller ΔJ. Using the MEG law, we found we need to include, as had PL in their fits to the infrared Q branches, an empirical dephasing scale factor F∼0.6 for the coherence transfer rates to obtain a satisfactory simulation of the R band head. PL suggested that dephasing in the Q branch spectra are due to cross relaxation across l-type doublet levels of the Π state, but no such mechanism would be available in the present case. However, we have found that by using a 50/50 linear combination of the ECS and MEG rate laws, it is possible to fit our data even with F=1, which would imply no dephasing of coherence. We take this as a demonstration that the dephasing factor F cannot be reliably extracted from line-mixing studies alone but instead requires some independent source of information on the relative value for state to state inelastic collision rates. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.471883

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West Antarctic Ice Sheet (WAIS) Divide ice core ultra-high resolution continuous CH4 measurements 67.2-9.8 ka BP (2017)

Rhodes, Rachael H ; Brook, Edward J ; Blunier, Thomas ; [et al.]

PANGAEA

In: Supplement to: Rhodes, Rachael H; Brook, Edward J; Chiang, John C H; Blunier, Thomas; Maselli, Olivia J; McConnell, Joseph R; Romanini, Daniele; Severinghaus, Jeffrey P (2015): Enhanced tropical methane production in response to iceberg discharge in the North Atlantic. Science, 348(6238), 1016-1019, https://doi.org/10.1126/science.1262005

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Publication Date: 2023-07-10

Description: Rhodes et al. 2015 (doi:10.1126/science.1262005) The causal mechanisms responsible for the abrupt climate changes of the Last Glacial Period remain unclear. One major difficulty is dating ice rafted debris (IRD) deposits associated with Heinrich events: Extensive icebergs influxes into the North Atlantic Ocean, linked to global impacts on climate and biogeochemistry. In a new ice core record of atmospheric methane with ultra-high temporal resolution, we find abrupt methane increases within Heinrich stadials 1, 2, 4 and 5 that, uniquely, have no counterparts in Greenland temperature proxies. Using a heuristic model of tropical rainfall distribution, we propose that Hudson Strait Heinrich events caused rainfall intensification over Southern Hemisphere land areas, thereby producing excess methane in tropical wetlands. Our findings suggest that the climatic impacts of Heinrich events persisted for 740 to 1520 years. --- Rhodes et al. 2017 (doi:10.1002/2016GB005570) In order to understand atmospheric methane (CH_4) biogeochemistry now and in the future, we must apprehend its natural variability, without anthropogenic influence. Samples of ancient air trapped within ice cores provide the means to do this. Here we analyze the ultrahigh-resolution CH_4 record of the West Antarctic Ice Sheet Divide ice core 67.2-9.8 ka and find novel, atmospheric CH_4 variability at centennial time scales throughout the record. This signal is characterized by recurrence intervals within a broad 80-50 year range, but we find that age-scale uncertainties complicate the possible isolation of any periodic frequency. Lower signal amplitudes in the Last Glacial relative to the Holocene may be related to incongruent effects of firn-based signal smoothing processes. Within interstadial and stadial periods, the peak-to-peak signal amplitudes vary in proportion to the underlying millennial-scale oscillations in CH_4 concentration-the relative amplitude change is constant. We propose that the centennial CH_4 signal is related to tropical climate variability that influences predominantly low-latitude wetland CH_4 emissions.

Type: Dataset

Format: application/zip, 5 datasets

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