Oscillator Strengths and Predissociation Widths for Rydberg Transitions

Oscillator Strengths and Predissociation Widths for Rydberg Transitions in CO between 930 and 935 Å S. R. Federman, Y. Sheffer (Univ. of Toledo) M. Eidelsberg, J. L. Lemaire, F. Rostas (Obs. de Paris, Meudon and Univ. de Cergy-Pontoisse) J. H. Fillion (Univ. UMPC, Paris VI) This research was supported by NASA and the CNRS-PCMI program

Introduction Background • CO observed in many astronomical environments – Diffuse and dark, molecular interstellar clouds – Circumstellar shells of asymptotic giant branch stars and planetary nebulae – Circumstellar disks around newly formed stars – Comets and planetary atmospheres

Introduction Processes affecting mix of isotopologues • Isotope Charge Exchange – favors 13 C 16 O – It has lower zero-point energy – 13 C+ + 12 C 16 O → 12 C+ + 13 C 16 O – ΔE (ΔE/k ≈ 35 K) • Selective Isotopic Photodissociation – favors more abundant isotopic variant – Dissociation occurs through line absorption at far UV wavelengths – More abundant variant has lines that are more optically thick, shielding itself from further dissociation

Introduction Hubble Space Telescope results on diffuse interstellar clouds Ratio X Per r Oph A χ Oph z Oph N(12 C 16 O)/N(13 C 16 O) 73± 12 125± 23 117± 35 167± 15 N(12 C 16 O)/N(12 C 18 O) 3000± 600 1000± 500 … 1550± 440 N(12 C 16 O)/N(12 C 17 O) 8700± 3600 … … ≥ 5900 IS Ratios: 12 C/13 C = 70± 7; 16 O/18 O = 560± 25; 16 O/17 O = 1900± 200

Introduction Problems • Detailed models can reproduce either the isotopologic ratios or the total column density, but not both with the same model • Models for diffuse molecular clouds produce too little CO Solution? • Part of the problem may lie in adopted oscillator strengths (f-values), which now seem too small for many important transitions – Small f-values lessen amount of self shielding, but need more self shielding

Our Previous Measurements on CO Federman et al. (2001, Ap. JS, 134, 133) • Used the Synchrotron Radiation Center of the Univ. of Wisconsin -Madison • Derived f-values for the B – X (0 -0), B – X (1 -0), C – X (0 -0), C – X (1 -0), and E – X (0 -0) bands (above 1075 Å) – Our results agree with other determinations based on electron energy loss and laser absorption

Our Previous Measurements on CO Far Ultraviolet Spectroscopic Explorer Observations HD 203374 A (Sheffer et al. 2003, Ap. J, 597, L 29)

Our Previous Measurements on CO Eidelsberg et al. (2004, A&A, 424, 355) • Used the SU 5 beam line at the Super. ACO Synchrotron in Orsay • Derived f-values for the K – X (0 -0), L′ – X (1 -0), L – X (0 -0) bands for 12 C 16 O, 13 C 16 O, and 13 C 18 O (967 – 972 Å) – There is significant mixing among bands, but sum of fvalues independent of isotopologue – First measurements on 13 C 18 O

Our Previous Measurements on CO Eidelsberg et al. (2006, Ap. J, 647, 1543) • Published additional data acquired on SU 5 beam line – Focus on the W – X (v′-0; v′=0 -3) bands as well as E – X (1 -0) and B – X (6 -0) bands [B – X (6 -0) formerly called F – X (0 -0) band] – Studied f-values and predissociation widths for 12 C 16 O, 13 C 16 O, and 13 C 18 O – Analysis based on profile syntheses that adjusted the band oscillator strength and line width (instrumental, thermal, and predissociation) in a non-linear least -squares fashion – Allowed for J-dependent predissociation widths

Oscillator Strengths for CO Comparison of Results for W – X Bands (f-value × 103) Reference (0 -0) (1 -0) 16. 6± 1. 6 16. 0± 1. 3 … 15. 8± 2. 0 Eidelsberg et al. 1991 (12 C 16 O) 12. 1± 1. 2 13. 5± 1. 4 25. 8± 2. 6 16. 3± 1. 6 Stark et al. 1992, 1993, 1994 (12 C 16 O) 12. 9± 1. 3 14. 8± 1. 5 30. 0± 3. 0 14. 9± 1. 5 Yoshino et al. 1995 (12 C 16 O) 13. 6± 2. 0 14. 8± 1. 5 20. 4± 3. 1 17. 0± 2. 6 Eidelsberg et al. 2006 (13 C 16 O) 15. 1± 0. 7 16. 1± 2. 8 30. 4± 1. 3 18. 7± 1. 4 Eidelsberg et al. 1991 (13 C 16 O) 13. 2± 1. 3 16. 1± 1. 6 27. 9± 2. 8 18. 7± 1. 9 Eidelsberg et al. 2006 (13 C 18 O) 13. 8± 2. 0 perturbed 29. 7± 4. 2 15. 4± 2. 4 Eidelsberg et al. 1991 (13 C 18 O) 13. 2± 1. 3 Eidelsberg et al. 2006 (12 C 16 O) Sheffer et al. 2003 (12 C 16 O) Italics: measurements at 20 K 16. 0± 1. 6 (2 -0) (3 -0) 30. 0± 2. 3 19. 7± 1. 4 23± 5 19. 8± 2. 4 27. 9± 2. 8 18. 6± 1. 9

Measurements at the SOLEIL Synchrotron • Used the DESIRS beamline with a VUV FTS

Measurements at the SOLEIL Synchrotron The FTS (de Oliveira et al. 2009, Rev. Sci. Instru. , 80, 043101) • Resolving power as high as 750, 000 • Based on wave front division instead of amplitude division • Relies on modified bimirror configuration requiring only flat mirrors • Path difference scanning through translation of one reflector

Measurements at the SOLEIL Synchrotron Preliminary results • Calibration band line profile – Used the B – X (0, 0) and (1, 0) bands for calibration [perturbations affect the E – X (0, 0) band W – X bands too strong] – Used an Airy function for the line shape

Measurements at the SOLEIL Synchrotron Preliminary results • Initial studies of series of bands between 930 and 935 Å in 12 C 16 O, 13 C 18 O, and 12 C 17 O (first measurements on 12 C 17 O) • Significant mixing is present – In 12 C 16 O have interactions among 4 pπ(2), II 1Π, 4 pσ(2), 5 pπ(0), 5 pσ(0), and I 1Π

Measurements at the SOLEIL Synchrotron Preliminary results

Measurements at the SOLEIL Synchrotron Preliminary results

Measurements at the SOLEIL Synchrotron Preliminary results Band (upper level) λ (Ǻ) f-values ( × 10 -3 ) limits Present E 91 S 91 Y 95 7. 3(0. 7) 6. 1(0. 9) 4 pp(2) 929. 7 -930. 8 7. 30 6. 3 II 1 P 930. 922 -932. 230 4. 59 930. 75§- 4 pσ(2) 931. 160 -932. 140 3. 13 5 pp(0) 931. 640 -933. 400 10. 85 Σ = 18. 57 b 5 ps(0) 932. 617 -933. 900 930. 75§- 21. 6(2. 2) 43. 9 17. 86 932. 58§ 8. 4(0. 8)a 933. 05§- I 1 P 933. 150 -934. 500 7. 89 Σ = 25. 75 c S 929. 7 -934. 5 51. 62 integrated limits value represents only the f-value of the R branch of 5 p b this is sum of II 1Π, 4 pσ(2), and 5 pπ(0) c this is sum of 5 pσ(0) and I 1Π § a this 16. 5(1. 6) 934. 5§ 50. 2 934. 5§ 53. 8(5. 4)

Future Work • Complete analysis on these bands, including a set of predissociation widths • With the improved spectral resolution, refine results for the W – X bands • Perform measurements with a cooled free jet (≈ 30 K) • A special focus on transitions in 12 C 17 O • Study many of the bands between 885 and 972 Å, especially those thought to be important for photodissociation in interstellar space