DETECTION OF THE AMMONIUM ION IN SPACE SUPPORTED BY AN IMPROVED DETERMINATION OF THE 1 0 − 0 0 ROTATIONAL FREQUENCY FROM THE 4 BAND OF NH 3 D + J. L. DOMÉNECH, M. CUETO, V. J. HERRERO & I. TANARRO, Molecular Physics Department, IEM-CSIC, Madrid, Spain; J. CERNICHARO & B. TERCERO, Department of Astrophysics, CAB. INTA-CSIC., Madrid, Spain; A.FUENTE, Observatorio Astronómico Nacional, Alcalá de Henares, Spain; N. MARCELINO, NRAO, Charlottesville, USA; E. ROUEFF, LUTH,Observatoire de Paris, CNRS UMR8102, Meudon, France; M. GÉRIN, LERMA, Observatoire de Paris, CNRS UMR8112 and École Normale Superieure, Paris, France; J. PEARSON, JPL, Pasadena, USA. J. L. Doménech et al. Detection of Ammonium in Space. WF05 68th Int. Symposium on Molecular Spectroscopy. Columbus 2013

41st Symposium on Molecular Spectroscopy : the Ohio State University, June 16-20, 1986

J. L. Doménech et al. Detection of Ammonium in Space. WF05 68th Int. Symposium on Molecular Spectroscopy. Columbus 2013 MOTIVATION A strong unidentified line at MHz in Orion- IRc2 1 From the analysis of the 4 infrared band of NH 3 D +, Nakanaga & Amano 2 predicted the transition at ±9 MHz (±3σ) No match with other known species in Orion. Is U NH 3 D + ? With yet 3500 unidentified lines in the Orion survey… too risky. 1 Tercero, B., Cernicharo, J., Pardo, J. R., & Goicoechea, J. R., 2010, A&A, 517, 96 2 Nakanaga, T., & Amano, T., 1986, Can. J. Phys., 64, 1356 N&A (1986)

J. L. Doménech et al. Detection of Ammonium in Space. WF05 68th Int. Symposium on Molecular Spectroscopy. Columbus 2013 Observations towards Sagitarius B1-b MHz /MHz Narrow and isolated feature (no more lines in 3.8 GHz) Kinetic temperature 12 K, the carrier has to be a light species NH 3, 15 NH 3, NH 2 D, 15 NH 2 D, ND 2 H, ND 3 have been detected, plus NNH +, NND +, 15 NNH+, N 15 NH + We need more laboratory evidence.

IR spectrometer: difference frequency mixing I 2 locked Ar + laser + Ring dye laser Spectral purity: ~1:10 8 (2 MHz) Accuracy: ~1 MHz Wavemeter for the dye laser (10 MHz) Tunability 2.2 – 4.2 µm ( cm -1 ) 1.2 cm -1 continuous scan Sensitivity: ~1: µW vs NEP of InSb First setup: Alan Pine (JOSA1976) Oka, Amano, Nesbitt… J. L. Doménech et al. Detection of Ammonium in Space. WF05 68th Int. Symposium on Molecular Spectroscopy. Columbus 2013

The discharge cell Hollow-cathode discharge Design Foster & McKellar(JCP1984) 380 V, 200 mA White cell ~9 m inside the cathode Discharge modulated at 5.5 kHz IR AM-modulated at 14.2 kHz Lock-in detection at 19.7 kHz Precursors: NH 3, D 2, 2:3 Total pressure 0.34 mbar

J. L. Doménech et al. Detection of Ammonium in Space. WF05 68th Int. Symposium on Molecular Spectroscopy. Columbus 2013 The whole set-up is very similar to the one used by Nakanaga & Amano CanJPhys (1986). Can we do any better? The main differences are: IR frequency scale: a Fizeau based wavemeter (see Toptica stand) (10 MHz, 3σ, accuracy, <2 MHz precision) for the dye laser in our case and a I 2 -stablized Ar + laser. IR= Ar+ - Dye Versus calibration with N 2 O IR absorption lines with ~1×10 −3 cm −1 (30 MHz) accuracy in N&A the rather different proportion of NH 3 and D 2 in the gas mixture ( ∼ 2:3 in our case vs. 1:10 in N&A), different absorption path lengths (9 m in this work vs. 20 m in N&A) the IR power available ( ∼ 1 μW in this work versus ∼ 10 μW in N&A) the detection at the sum frequency vs. detection at the discharge frequency, and the different discharge frequencies (5.5 kHz versus 17 kHz), The temperature: 315 K vs. 200K?

J. L. Doménech et al. Detection of Ammonium in Space. WF05 68th Int. Symposium on Molecular Spectroscopy. Columbus 2013 This work Nakanaga & Amano (1986) Lines marked with * belong to NH 4 + Rather similar S/N

J. L. Doménech et al. Detection of Ammonium in Space. WF05 68th Int. Symposium on Molecular Spectroscopy. Columbus 2013 NH4+ Schafer, Saykally, Robiette 1984, JChemPhys 80, 3969 This work Both this work and N&A Simulations and fits have been done with PGOPHER. (Colin Western, University of Bristol, ttp://pgopher.chm.bris.ac.uk )ttp://pgopher.chm.bris.ac.uk We have been guided by Nakanaga & Amano previous work.

J. L. Doménech et al. Detection of Ammonium in Space. WF05 68th Int. Symposium on Molecular Spectroscopy. Columbus 2013 NH4+ Schafer, Saykally, Robiette 1984, JChemPhys 80, 3969 This work Both this work and N&A

J. L. Doménech et al. Detection of Ammonium in Space. WF05 68th Int. Symposium on Molecular Spectroscopy. Columbus 2013 We have recorded 114 transitions between and cm -1 Finally 76 have been included in the fit (vs. 61 in N&A) Lines not included: J,K >8; or show interference from NH 4 +, NH 3 ; or are too broad A’, A’’, D K ’, D K ’’,  Cannot be determined independently. Constraining A’’, D K ’’ affects 0, , A’, D K ’ s.d. of the fit 5×10 -4 cm -1

J. L. Doménech et al. Detection of Ammonium in Space. WF05 68th Int. Symposium on Molecular Spectroscopy. Columbus 2013 N&A (1986 ) We believe that our dye laser frequencies are good to ~10 MHz (3.3×10 -4 cm -1 )(3σ), but, actually reproducibility and internal coherence are ~ 3 MHz (1×10 -4 cm -1 ) Our Ar + laser is locked to an I 2 line known with 0.1 MHz accuracy We have measured some more lines than in N&A work All statistical parameters are somewhat better We propose ±6 MHz as the frequency of the rotational transition of NH 3 D +,, thus supporting the assignment of emission lines s in Orion IRc2 and Sagitarius B1b to NH 3 D + (Astrophysical Journal Letters, Cernicharo et al and Doménech et al 2013, online yesterday. Vol 771, L10, L11) º±3σ NH 3 D +