1. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 NEW ACCURATE WAVENUMBERS OF H 35 Cl + AND H 37 Cl + ROVIBRATIONAL TRANSITIONS IN THE v= 0-1 BAND OF THE 2 Π STATE José Luis Doménech, Maite Cueto, Isabel Tanarro, Víctor José Herrero, Instituto de Estructura de la Materia CSIC (Madrid, Spain) José Cernicharo Instituto de Ciencia de Materiales CSIC (Madrid, Spain) Brian Drouin Jet Propulsion Laboratory NASA (Pasadena, USA)

2. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Motivation HCl + is a key intermediate in the chlorine chemistry in ISM. HCl + has been detected recently in the mm-wave region both in space (Herschel) and in the laboratory (De Luca et al. ApJ751,L37,2012 & Gupta el al ApJL 751, L38, 2012) There is plenty of spectroscopic information from the vis-UV 1 but of it is of limited accuracy (0,04 cm -1 ), and is scarce in the submm-wave 2 and IR 3 regions. The JPL group has performed an isotope-independent global fit of mm-wave and optical data, but with no IR data. 2 Π 3/2 J=5/2-3/2 transition @ 1.44 THz. Impossible to be observed from ground. Future studies or astronomical searches from ground will benefit from more accurate IR information. 1 Sheashley JMS 47, 420, (1973) 2 FIR LMR by Lubic et al. (1989), Gupta et al. ApJL (2012) 3 MIR LMR DCl + by Hinz et al. (1984), DL-IR by Davies et al. (1986).

3. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Background HCl + is open-shell with S=1/2 G.s. is an inverted 2 Π, 2 Π 3/2 is 644 cm -1 lower in energy than 2 Π 1/2 Spin-orbit coupling, Λ doubling and hyperfine interaction with 35 Cl and 37 Cl (nuclear spin I=3/2) and H (I=1/2) 12,5 11,5 10,5 9,5 8,5 7,5 6,5 5,5 4,5 0,5 1,5 2,5 3,5 e f e f 12,5 11,5 10,5 9,5 8,5 7,5 6,5 5,5 4,5 1,5 3,5 2,5 Sub-mm-wave transitions observed in the lab e f e f e f e f e f e f 12,5 11,5 10,5 9,5 8,5 7,5 6,5 5,5 4,5 0,5 1,5 2,5 3,5 12,5 11,5 10,5 9,5 8,5 7,5 6,5 5,5 4,5 1,5 3,5 2,5 J J J J P Q RP Q R P Q RP Q R Herschel HIFI obsevation. Taken from DeLuca et al

4. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Previous studies: More than 8100 lines of 35 HCl + and 37 HCl + with 0,04-0,05 cm -1 accuracy A 2 Σ +- X 2 Π

5. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Previous studies (2) Gupta, H., Drouin, B. J., & Pearson, J. C. (2012). THE ROTATIONAL SPECTRUM OF HCl +. ApJL, 751(2), L38. 24 mm-wave lines with better than 150 kHz accuracy Global Dunham-type isotope independent fit together with optical data. Predictions for v=1-0.

6. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Previous studies (3): IR diode laser absorption in an ac discharge and velocity modulation: Davies, P. B., Hamilton, P. A., & Johnson, S. A. (1986). “Velocity modulation detection of HCl +.” Mol. Phys. 57(1), 217–220. 16 lines with ~0,002 cm -1 accuracy

7. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Experimental: IR difference frequency source First setup: Alan Pine (1976) I 2 locked Ar + laser & Ring dye laser Mixing in PP LiNbO 3 (DFG) Spectral purity: ~1:10 8 (2 MHz) Tunability 2.4 – 5.5 µm (1800-4200 cm -1 ) 1.2 cm -1 continuous scan S/N in transmission: 2000 ~1 mW SS Wavemeter for the dye laser. Accuracy: ~3 MHz (1σ) At each datapoint in the spectrum, we have an ‘instantaneous’ wavemeter reading. The wavemeter is calibrated with the Ar + laser. We can average a lot of scans.

8. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Experimental: the discharge cell Hollow-cathode discharge Design: Dymanus, (Foster & McKellar) 600 V, 300 mA White cell ~22 m inside the cathode Current modulated at f 1 =3.09 kHz IR modulated at f 2 =23.19 kHz Lock-in detection at f 1 +f 2 =26,28 kHz Autobalanced subtractive amplifier (Lindsay PhD diss., 2001) Precursors: HCl/He: 0.002 mbar/ 2 mbar Water cooled (~50 ºC) Adapted from Amano, Proc RSL 1988

9. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Results 178 lines recorded between 2337-2774 cm -1 For each line, between 6 to 150 averages to attain a 10 < S/N<2000 We have used the predictions from Sheashley’s polinomial expressions

10. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Results IR diode data (Davies 1986)

11. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Results Several lines present partially resolved nuclear hyperfine structure, or unresolved structure, or just asymmetry.

12. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Preliminary fits Assignment has been obvious with Sheashley and JPL data. Although it is a “reasonable” Hund’s a-coupling case (A/B = -66) we have used the following effective Hamiltonian, integrated in the SPFIT program (Pickett 1991, Drouin 2001): B, D, H, A, p, q, γ can be expressed as

13. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Preliminary fits We have performed fits of the IR data alone, before including them in the global fit. Dataset is consistent, except for ~18 lines.

14. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Preliminary global fit 8102 UV-vis frequencies, 34 sub-mm wave frequencies and 160 IR lines have been fit to an effective Hamiltonian. 70 independent parameters ( 2 Π and 2 Σ states). Almost all of the new IR lines can be fitted within experimental accuracy. The rest are obvious blends or, potentially, proton hyperfine structure. The new fit has allowed the determination of A H, Δ 01 (Cl) and Δ 10 (Cl). A H has proven essential. Results are preliminary: new measurements with refined S/N and lower T will likely improve the information on the proton hfs.

15. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Preliminary global fit

16. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Summary We have provided accurate (1σ ≤ 0,0003 cm -1 ~ 3 MHz) wavenumbers for 178 IR transitions of H 35 Cl + and H 37 Cl +, most of them measured for the first time. 160 fitted. The nuclear hyperfine structure is partially resolved for a number of low-J lines. All but a few can be fit with the current hf parameters. There is some evidence of Hydrogen hfs. New measurements at lower T will likely provide new information on the proton hyperfine interaction constants. Results are preliminary, …more work is underway. Caveat: Classic toys still create a lot of fun.

17. José Luis Doménech, RD08 70th International Symposium on Molecular Spectroscopy Urbana Champaign, June 22-26,2015 Acknowledgements Coworkers: Maite Cueto, Isabel Tanarro, Víctor J. Herrero, José Cernicharo & Brian Drouin. Funding: Ministry of Economy and Competitiveness CONSOLIDER Astromol CDS2009-00038, FIS2010-16455, FIS 2012-38175