Oscillator Strengths and Predissociation Widths for Rydberg Transitions in Carbon Monoxide (original) (raw)
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Predissociation of the 4pπL1Π Rydberg state of carbon monoxide
Chemical Physics, 2002
Time-domain and frequency-domain spectroscopic experiments have been performed on the ð4ppÞL 1 P, v ¼ 0 Rydberg state in three isotopomers of carbon monoxide. Accurate values for the excited state lifetimes of the f-parity components have been determined: sð 12 C 16 OÞ ¼ 1:08 AE 0:05 ns, sð 13 C 16 OÞ ¼ 72 AE 10 ps and sð 13 C 18 OÞ ¼ 29 AE 6 ps. The spectral resolution in the frequency-domain experiment goes as far as the limit imposed by the natural lifetime; Qbranch 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.
Oscillator Strengths for B – X , C – X , and E – X Transitions in Carbon Monoxide
The Astrophysical Journal Supplement Series, 2001
Band oscillator strengths for electronic transitions in CO were obtained at the Synchrotron Radiation Center of the University of Wisconsin-Madison. Our focus was on transitions that are observed in interstellar spectra with the Far Ultraviolet Spectroscopic Explorer; these transitions are also important in studies of selective isotope photodissociation where fractionation among isotopomers can occur. Absorption from the ground state (X 1 Σ + v ′′ = 0) to A 1 Π (v ′ = 5), B 1 Σ + (v ′ = 0, 1), C 1 Σ + (v ′ = 0, 1), and E 1 Π (v ′ = 0) was measured. Fits to the A − X (5, 0) band, whose oscillator strength is well known, yielded the necessary column density and excitation temperature. These parameters were used in a least-squares fit of the observed profiles for the transitions of interest to extract their band oscillator strengths. Our oscillator strengths are in excellent agreement with results from recent experiments using a variety of techniques. This agreement provides the basis for a self-consistent set of f-values at far ultraviolet wavelengths for studies of interstellar (and stellar) CO.
Predissociation of the 4ppLP Rydberg state of carbon monoxide
2002
Time-domain and frequency-domain spectroscopic experiments have been performed on the ð4ppÞLP, v 1⁄4 0 Rydberg state in three isotopomers of carbon monoxide. Accurate values for the excited state lifetimes of the f-parity components have been determined: sðCOÞ 1⁄4 1:08 0:05 ns, sðCOÞ 1⁄4 72 10 ps and sðCOÞ 1⁄4 29 6 ps. The spectral resolution in the frequency-domain experiment goes as far as the limit imposed by the natural lifetime; Qbranch 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. 2002 Elsevier Science B.V. All rights reserved.
The Astrophysical Journal, 2006
One of the processes controlling the interstellar CO abundance and the ratio of its isotopologues is photodissociation. Accurate oscillator strengths and predissociation rates for Rydberg transitions are needed for modeling this process. We present results on absorption from the E 1 Π − X 1 Σ + (1-0) and B 1 Σ + − X 1 Σ + (6-0) bands at 1051 and 1002Å, respectively, and the vibrational progression W 1 Π − X 1 Σ + (v ′ -0) bands with v ′ = 0 to 3 at 972, 956, 941, and 925Å, respectively. The corresponding spectra were acquired at the high resolution (R ≈ 30,000) SU5 beam line at the Super ACO Synchrotron in Orsay, France. Spectra were obtained for the 12 C 16 O, 13 C 16 O, and 13 C 18 O isotopologues. These represent the most complete set of measurements available. Comparison is made with earlier results, both empirical and theoretical. While earlier determinations of oscillator strengths based on absorption from synchrotron radiation tend to be somewhat smaller than ours, the suite of measurements from a variety of techniques agree for the most part considering the mutual uncertainties. For the bands studied here, their relative weakness, or their significant line widths arising from predissociation, minimizes potential problems from large optical depths at line center in absorption measurements. Predissociating line widths could generally be extracted from the spectra thanks to the profile simulations used in the analysis. In many cases, these simulations allowed us to consider e and f parity levels separately and to determine the dependence of the width on rotational quantum number, J. Our results are consistent with earlier determinations, especially the widths inferred from laser experiments.
The Journal of Chemical Physics, 2005
Two new red-degraded bands in the room-temperature vacuum-ultraviolet absorption spectrum of carbon monoxide have been identified in the 94 000-94 500 cm −1 energy region and analyzed. One of the bands at Ϸ94 225 cm −1 ͑106.1 nm͒ has three observable bandheads and is partially overlapped with the strong C 1 ⌺ +-X 1 ⌺ + ͑1-0͒ transition at lower energy. It is assigned to the c 3 ⌸-X 1 ⌺ + ͑1-0͒ transition. The other band at Ϸ94 437 cm −1 ͑105.9 nm͒ with one clear bandhead is assigned to the k 3 ⌸-X 1 ⌺ + ͑5-0͒ transition. A strong homogeneous perturbation was found to exist between the two upper states that strongly influences the line positions and shapes of these bands. A rotational deperturbation analysis was performed and molecular rotational constants for both upper states were determined. These deperturbed molecular constants are entirely consistent with the expected values for the k 3 ⌸ valence and c 3 ⌸ Rydberg states. The Hamiltonian interaction term between these two states is found to be separable into vibrational and electronic factors and the electronic factor is determined to be H e = 323± 40 cm −1. A discrepancy in the literature regarding the location of the c 3 ⌸ ͑v =1͒ state is identified and discussed.
The Astrophysical Journal, 1997
We have detected the J = 4 ← 3 rotational transition of 12 CO in absorption at z = 0.89 towards the quasar PKS 1830−211, but not the 12 CO (5 ← 4) or the 3 P 1 ← 3 P 0 fine structure line of neutral carbon. The intervening molecular medium thus has a total 12 CO column density of 10 18 cm −2 ≤ N (CO) ≤ 5 × 10 18 cm −2 with a most likely value of N (CO) ≃ 2 × 10 18 cm −2 , which corresponds to the large column density of molecular hydrogen of N (H 2 )= 2.5 × 10 22 cm −2 and a reddening of A v = 25 magnitudes. The 12 CO excitation temperature is low, below 15 K. Comparison with the molecular absorption results of shows that the absorbing material has similar molecular abundances to Galactic dark clouds. We find an upper limit for atomic carbon of N (Ci)≤ 10 18 cm −2 , which again would be the case for most Galactic dark clouds.
High-resolution study of oscillator strengths and predissociation rates for12C16O
Astronomy & Astrophysics, 2012
Models of astronomical environments containing CO require accurate molecular data to reproduce and interpret observations. We are conducting experiments at the SOLEIL synchrotron facility to acquire data for modeling CO photochemistry in the vacuum ultraviolet. The improvement in UV spectroscopic instrumentation, both in sensitivity and resolution, provides more accurate laboratory spectroscopic determinations. We report new measurements yielding photoabsorption oscillator strengths and predissociation rates, for 12 C 16 O at 295 K and 77 K, of four bands from X 1 Σ + (v = 0) to the v = 0-3 vibrational levels of the core-excited W 1 Π Rydberg state and for six overlapping bands between 92.97 and 93.35 nm. Absorption spectra were recorded using the vacuum ultraviolet Fourier transform spectrometer installed on the DESIRS beamline at SOLEIL, providing a resolving power R = 350 000. This resolution allows the analysis of individual line strengths and widths in the electronic transitions and the identification of a previously unobserved perturbation in the W(1) level. Gas column densities in the differentially-pumped system were calibrated using the B 1 Σ +-X 1 Σ + (0, 0) band. Absorption bands are analyzed by synthesizing line and band profiles with independently developed codes. These considerably improved results are compared with earlier determinations.
The Journal of Chemical Physics, 2004
Rotationally cold absorption and two-photon ionization spectra of CO in the 90–100 nm region have been recorded at a resolution of 0.3–1.0 cm−1. The analyses of up to four isotopomers seek to clarify the observations in regions where the Rydberg levels built on the ground state X 2Σ+ of the ion interact with valence states of 1Σ+ and 1Π symmetry. Previous observations of the 3sσ, B 1Σ+ Rydberg state, reviewed by Tchang-Brillet et al. [J. Chem. Phys. 96, 6735 (1992)], have been extended to energies above its avoided crossing with the repulsive part of the D′ 1Σ+ valence state where resonances of varying intensities and widths have been attributed to the fully coupled 3sσ or 4sσ and D′ potentials, and where the B state approaches a second avoided crossing with the C′ 1Σ+ valence state [Cooper and Kirby, J. Chem. Phys. 87, 424 (1987); 90, 4895 (1989); Chem. Phys. Lett. 152, 393 (1988)]. Fragments of a progression of weak and mostly diffuse bands, observed for all four isotopomers, have...
Isotope dependent predissociation in the C1Σ+, v=0 and v=1 states of CO
The European Physical Journal D, 2001
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 derived and no effects of perturbation are found at the present level of accuracy. Line broadening measurements result in information on the excited state lifetime of the C 1 Σ + , v = 1 state for five natural isotopomers of carbon monoxide: τ ( 12 C 17 O) = 280 ps, τ ( 12 C 18 O) = 210 ps, τ ( 13 C 16 O) = 295 ps, τ ( 13 C 17 O) = 160 ps, and τ ( 13 C 18 O) = 150 ps. Within the accuracy of the present measurements no 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 Σ + , v = 0 and v = 1 states of the main isotopomer are performed in a pump-probe experiment using a picosecond VUV-laser, yielding τ ( 12 C 16 O) = 1780 ps for v = 0 and τ ( 12 C 16 O) = 625 ps for v = 1. For C 1 Σ + , v = 0 in 12 C 16 O and 13 C 16 O the same lifetime is found; this lifetime matches experimental values of the oscillator strength and hence supports previous results showing pure radiative decay in this state; the error margins however do not exclude some low level of predissociation. The measurements indicate that the C 1 Σ + , v = 0 state of the 13 C 18 O isotopomer is predissociated with an estimated yield of 17% (i.e. above the level of predissociation for 12 C 16 O.) From the combined data predissociation yields upon excitation of the C 1 Σ + , v = 1 state are derived, lying in the range 0.84-0.91 for the five less abundant isotopomers; for the main 12 C 16 O isotopomer a strongly deviating predissociation yield of 0.65 is deduced.