| 1. |
- Ubachs, W, et al.
(författare)
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Lifetime measurements on the c '(1)(4)Sigma(+)(u), v=0, 1 and 2 states of molecular nitrogen
- 2001
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Ingår i: Chemical Physics. - 0301-0104. ; 270:1, s. 215-225
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Tidskriftsartikel (refereegranskat)abstract
- Excited state lifetimes of c(4)('1)Sigma (+)(u), upsilon = 0-2 states of molecular nitrogen have been determined in a laboratory investigation using a picosecond XUV laser in a pump-probe configuration. For c(4)('1)Sigma (+)(u) upsilon = 0 the lifetime is tau = 740 +/- 50 ps, for the lowest rotational states. For higher rotational states a gradual shift towards tau = 495 ps is found in agreement with previous findings that these states are subject to predissociation. For c(4)(') Sigma (+)(u) upsilon = 1 no J-dependence is found and values for two isotopomers are reported: tau = 240 ps for (NN)-N-14-N-15 = 240 ps for (NN)-N-14-N-15. For c(4)('1)Sigma (+)(u) upsilon = 2 a lifetime for the lowest rotational states (J = 0-3) was derived: tau = 675 +/- 50 ps; for J = 11 a lifetime of tau less than or equal to 120 ps is deduced. All values for the lifetimes including the J-dependences are explained in a model based on Rydberg-valence interaction. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 2. |
- Cacciani, P, et al.
(författare)
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Isotope dependent predissociation in the C-1 Sigma(+) ,v=0 and v=1 states of CO
- 2001
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Ingår i: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060. ; 15:1, s. 47-56
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Tidskriftsartikel (refereegranskat)abstract
- Rotationally resolved spectral lines in the C-X(1,0) band of carbon monoxide are investigated under high resolution using a coherent vacuum ultraviolet laser source, continuously tunable near 107 nm. Transition frequencies are determined by calibrating against a reference standard of iodine lines, recorded with saturation spectroscopy in the visible range, yielding an absolute accuracy of 0.003 cm(-1) in the vacuum ultraviolet. Improved molecular constants for the excited state are clarified and Mo effects of perturbation are found at the present level of accuracy. Line broadening measurements result in information on the excited state lifetime of the (CC)-C-1 Sigma (+),v = 1 state fur five natural isotopomers: of cal bon monoxide: tau((CO)-C-12-O-17) = 280 ps, tau((CO)-C-12-O-18) = 210 ps. tau((CO)-C-13-O-16) = 295 ps, tau((OO)-O-13-O-17) = 160 ps and tau((CO)-C-13-O-18) = 150 Ps. Within the accuracy of the present measurements: Ilo effects: of J-dependent lifetimes: were observed, for neither of the isotopomers. In addition direct time domain measurements: of the lifetime of the C(1)Sigma (+),v = 0 and v = 1 states of the main isotopomer are performed ill a pump-mode experiment using a picosecond VUV-laser, yielding tau((CO)-C-12-O-16) = 1780 ps for v = 0 and tau((CC)-C-12-C-16)) = 625 ps for v = 1. For C(1)Sigma (+), v = 0 in (CO)-C-12-O-16 and (CO)-C-13-O-16 the same lifetime is found; this lifetime matches experimental values of the oscillator strength and hence supports previous results showing pure radiative decay ill this state; the error margins however do not exclude some low level of predissociation. The measurements indicate that the C(1)Sigma (+),v = 0 state of the (CO)-C-13-O-18 isotopomer is predissociated with an estimated yield of 17% (i.e. above the level of predissociation for (CO)-C-12-O-16.) From the combined data predissociation yields: upon excitation of the C(1)Sigma (+),v = 1 state are derived, lying in the range 0.84-0.91. for the five less abundant isotopomers; for the main (CO)-C-12-O-16 isotopomer a strongly deviating predissociation yield of 0.65 is deduced.
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| 3. |
- Cacciani, P, et al.
(författare)
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Lifetime measurements of the E (1)Pi, upsilon=0 and upsilon=1 states of (CO)-C-12-O-16, (CO)-C-13-O-16, and (CO)-C-13-O-18
- 1998
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X. ; 499
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Tidskriftsartikel (refereegranskat)abstract
- In a laboratory investigation using tunable picosecond lasers in a pump-probe configuration, lifetimes of the E (II)-I-1, v = O and v = 1 states of CO are experimentally determined. For E (II)-I-1, v = 1, the lifetime is found to vary significantly for the isotopomers. Combining the data with existing oscillator strengths, predissociation probabilities within the range of 93.6%-98.64% result for (CO)-C-12-O-16, (CO)-C-13-O-16, and (CO)-C-13-O-18 in, the case of the E (II)-I-1, v=1 state, which is the state that predominantly influences the isotopic fractionation of CO in interstellar clouds.
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| 4. |
- Cacciani, P., et al.
(författare)
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Lifetime measurements of the e1II, v = 0 and v = 1 states of12C16O, 13C16O, and13C18O
- 1998
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Ingår i: Astrophysical Journal. - 0004-637X. ; 499:2 PART II, s. 223-226
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Tidskriftsartikel (refereegranskat)abstract
- In a laboratory investigation using tunable picosecond lasers in a pump-probe configuration, lifetimes of the E 1u, v = 0 and v = 1 states of CO are experimentally determined. For E 'D, v = 1, the lifetime is found to vary significantly for the isotopomers. Combining the data with existing oscillator strengths, predissociation probabilities within the range of 93.6%-98.6% result for 12C16O, 13C16O, and 13C18O in the case of the E 1u, v = I state, which is the state that predominantly influences the isotopic fractionation of CO in interstellar clouds.
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| 5. |
- Cacciani, P, et al.
(författare)
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Predissociation of the 4p pi L-1 Pi Rydberg state of carbon monoxide
- 2002
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Ingår i: Chemical Physics. - 0301-0104. ; 282:1, s. 63-73
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Tidskriftsartikel (refereegranskat)abstract
- Time-domain and frequency-domain spectroscopic experiments have been performed on the (4ppi)L(1)Pi, v = 0 Rydberg state in three isotopomers of carbon monoxide. Accurate values for the excited state lifetimes of the f-parity components have been determined: tau((CO)-C-12-O-16) = 1.08 +/- 0.05 ns, tau((CO)-C-13-O-16) = 72 +/- 10 ps and tau((CO)-C-13-O-18) = 29 +/- 6 ps. The spectral resolution in the frequency-domain experiment goes as far as the limit imposed by the natural lifetime; Q-branch lines, or f-parity components of the heavier isotopes, are resolved for the first time. Highly accurate transition frequencies are determined in a molecular beam experiment using comparison and interpolation with a saturated iodine reference standard. The results reveal a number of perturbations and predissociation mechanisms, displaying a high degree of complexity in the energetic region of the 4p Rydberg states of CO with strong isotopic effects. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 6. |
- Dapra, M, et al.
(författare)
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Testing the variability of the proton-to-electron mass ratio from observations of methanol in the dark cloud core L1498
- 2017
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 472:4, s. 4434-4443
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Tidskriftsartikel (refereegranskat)abstract
- The dependence of the proton-to-electron mass ratio, μ, on the local matter density was investigated using methanol emission in the dense dark cloud core L1498. Towards two different positions in L1498, five methanol transitions were detected and an extra line was tentatively detected at a lower confidence level in one of the positions. The observed centroid frequencies were then compared with their rest-frame frequencies derived from least-squares fitting to a large data set. Systematic effects, as the underlying methanol hyperfine structure and the Doppler tracking of the telescope, were investigated and their effects were included in the total error budget. The comparison between the observations and the rest-frame frequencies constrains potential μ variation at the level of Δμ/μ
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| 7. |
- Kanekar, N., et al.
(författare)
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Constraints on changes in the proton-electron mass ratio using methanol lines
- 2015
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Ingår i: Monthly Notices of the Royal Astronomical Society: Letters. - : Oxford University Press (OUP). - 1745-3925 .- 1745-3933. ; 448:1, s. L104-L108
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Tidskriftsartikel (refereegranskat)abstract
- We report Karl G. Jansky Very Large Array (VLA) absorption spectroscopy in four methanol (CH3OH) lines in the z = 0.885 82 gravitational lens towards PKS1830-211. Three of the four lines have very different sensitivity coefficients K-mu to changes in the proton-electron mass ratio mu; a comparison between the line redshifts thus allows us to test for temporal evolution in mu. We obtain a stringent statistical constraint on changes in mu by comparing the redshifted 12.179 and 60.531 GHz lines, [Delta mu/mu] 4 sigma significance). The sensitivity of the above result, and that of all earlier CH3OH studies, is thus likely to be limited by unknown systematic errors, probably arising due to the frequency-dependent structure of PKS1830-211. A robust result is obtained by combining the three lines at similar frequencies, 48.372, 48.377 and 60.531 GHz, whose line profiles are found to be in good agreement. This yields the 2 sigma constraint [Delta mu/mu] less than or similar to 4 x 10(-7), the most stringent current constraint on changes in mu. We thus find no evidence for changes in the proton-electron mass ratio over a lookback time of approximate to 7.5 Gyr.
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| 8. |
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| 9. |
- Muller, Sebastien, 1976, et al.
(författare)
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A study of submillimeter methanol absorption toward PKS 1830-211:: Excitation, invariance of the proton-electron mass ratio, and systematics
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 652
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Tidskriftsartikel (refereegranskat)abstract
- Context. Methanol is an important tracer to probe physical and chemical conditions in the interstellar medium of galaxies. Methanol is also the most sensitive target molecule for probing potential space-time variations of the proton-electron mass ratio, μ, a dimensionless constant of nature. Aims. We present an extensive study of the strongest submillimeter absorption lines of methanol (with rest frequencies between 300 and 520 GHz) in the z = 0.89 molecular absorber toward PKS 1830-211, the only high-redshift object in which methanol has been detected. Our goals are to constrain the excitation of the methanol lines and to investigate the cosmological invariance of μ based on their relative kinematics. Methods. We observed 14 transitions of methanol, five of the A-form and nine of the E-form, and three transitions of A-13CH3OH, with ALMA. We analyzed the line profiles with a Gaussian fitting and constructed a global line profile that is able to match all observations after allowing for variations of the source covering factor, line opacity scaling, and relative bulk velocity offsets. We explore methanol excitation by running the non local thermal equilibrium radiative transfer code RADEX on a grid of kinetic temperatures and H2 volume densities. Results. Methanol absorption is detected in only one of the two lines of sight (the southwest) to PKS 1830-211. There, the excitation analysis points to a cool (∼10 - 20 K) and dense (∼104 - 5 cm-3) methanol gas. Under these conditions, several methanol transitions become anti-inverted, with excitation temperatures below the temperature of the cosmic microwave background. In addition, we measure an abundance ratio A/E = 1.0 ± 0.1, an abundance ratio CH3OH/H2 ∼ 2 × 10-8, and a 12CH3OH/13CH3OH ratio 62 ± 3. Our analysis shows that the bulk velocities of the different transitions are primarily correlated with the observing epoch due to morphological changes in the background quasar's emission. There is a weaker correlation between bulk velocities and the lower level energies of the transitions, which could be a signature of temperature-velocity gradients in the absorbing gas. As a result, we do not find evidence for variations of μ, and we estimate Δμ/μ=(-1.8 ± 1.2) × 10-7 at 1-σ from our multivariate linear regression. Conclusions. We set a robust upper limit |Δμ/μ| < 3.6 × 10-7 (3σ) for the invariance of μ at a look-back time of half the present age of the Universe. Our analysis highlights that systematics need to be carefully taken into account in future radio molecular absorption studies aimed at testing Δμ/μ below the 10-7 horizon.
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| 10. |
- Schulz, A., et al.
(författare)
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The inhomogeneous ISM toward PKS 1830–211 SW: A detailed view of molecular gas at a look-back time of 7.5 Gyr
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 574, s. 108-
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Tidskriftsartikel (refereegranskat)abstract
- Based on measurements with the Effelsberg 100-m telescope, a multiline study of molecular species is presented toward the southwestern source of the gravitational lens system PKS 1830–211, which is by far the best known target for studying molecular gas in absorption at intermediate redshift. Determining line parameters and optical depths and performing large velocity gradient radiative transfer calculations, the aims of this study are (1) to evaluate physical parameters of the absorbing foreground gas at z ~ 0.89, in particular its homogeneity; and (2) to monitor the spectroscopic time variability caused by fluctuations in the z ~ 2.5 background continuum source. We find, that the gas is quite inhomogeneous with n(H2) ~ 2 × 103 cm-3 for most molecular species but with higher values for H2CO and lower ones for SO. Measuring the CS J = 1 ← 0 transition during a time interval of more than a decade, from 2001 to 2012, the peak absorption depth of the line remains approximately constant, while the line shape undergoes notable variations. Covering the time between 1996 and 2013, CS, HCO+, and CH3OH data indicate maximum integrated optical depths in ~2001 and 2011/2012. This is compatible with a ~10 yr periodicity, which, however, needs confirmation by substantially longer time monitoring. Comparing molecular abundances with those of different types of Galactic and nearby extragalactic clouds we find that the observed cloud complex does not correspond to one particular type but to a variety of cloud types with more diffuse and denser components as can be expected for an observed region with a transverse linear scale of several parsec and a likely greater depth along the line of sight. A tentative detection of Galactic absorption in the c-C3H2 110−101 line at 18.343 GHz is also reported.
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