HighResolution Spectroscopy on Doubly Deuterated Ammonia up to

High-Resolution Spectroscopy on Doubly Deuterated Ammonia up to 2. 6 THz 61 st International Symposium on Molecular Spectroscopy, Ohio State University Christian Endres

Overview • Motivation • Spectrometer Setup • Measurements on ND 2 H • Conclusion Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres

Motivation Astrophysical Relevance Deuterium fractionation has become an important topic in dark clouds Cosmic abundance: D/H ~ 1. 4 x 10 -5, but NH 2 D / NH 3 ~ 0. 1 ND 2 H / NH 2 D ~ 0. 05 ND 3 / ND 2 H ~ 0. 02 First interstellar detections of the ammonia isotopic species: NH 3: 1968 NH 2 D: 1978 ND 2 H: 2000 ND 3: 2002 Light hydrides such as ammonia and its isotopic species have strong transitions in the THz region Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres

Motivation New Telescopes for the THz-region: CONDOR / APEX Atacama Pathfinder Experiment 1. 3 -1. 5 THz First Light Oct. 2005 GREAT / SOFIA Stratospheric Observatory For Infrared Astronomy 1. 6 -1. 9 THz and 2. 4 – 2. 7 THz scheduled 2008 HIFI / Herschel Space Observatory 0. 5 - 1. 25 THz and 1. 4 - 1. 9 THz Start Aug 2008 Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres

Motivation Previous works Laboratory spectroscopic investigations on ND 2 H: Large dataset of microwave transitions up to 515 GHz and quantitative description of the inversion - rotation spectra De Lucia & Helminger, J. Mol. Spectrosc. 54 (1975) 200 -214 Improvement of the Hamiltonian, analysis of both inversion substates simultaneously and determination of structural parameters Cohen & Pickett, J. Mol. Spectrosc. 93 (1982) 83 -100 Large dataset of FIR transition frequencies up to 220 cm-1 (6. 6 THz) (+ some MW lines) Fusina et al. , J. Mol. Spectrosc. 127 (1988) 240 -254 Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres

ND 2 H Spectrum Asymmetric top = − 0. 2284 (prolate) Inversion causes splitting into lower symmetric and upper asymmetric substates Each inversion doublet consists of one ortho- and one para- state Weak b-type transitions within inversion substates ( b =0. 21 D) Strong c-type transitions between inversion substates ( c =1. 47 D ) Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres

ND 2 H Spectrum Asymmetric top = − 0. 2284 (prolate) Inversion causes splitting into lower symmetric and upper asymmetric substates Each inversion doublet consists of one ortho- and one para- state Weak b-type transitions within inversion substates ( b =0. 21 D) Strong c-type transitions between inversion substates ( c =1. 47 D ) Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres

ND 2 H Spectrum 220 221 40 211 10 0 c-type 20 212 202 b-type E [cm-1] 30 para ortho Asymmetric top = − 0. 2284 (prolate) Inversion causes splitting into lower symmetric and upper asymmetric substates Each inversion doublet consists of one ortho- and one para- state 110 111 101 Weak b-type transitions within inversion substates ( b =0. 21 D) 000 Strong c-type transitions between inversion substates ( c =1. 47 D ) Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres

ND 2 H Spectrum Asymmetric top = − 0. 2284 (prolate) 1 Intensity [ a. u. ] 0. 8 Inversion causes splitting into lower symmetric and upper asymmetric substates 0. 6 Each inversion doublet consists of one ortho- and one para- state 0. 4 Weak b-type transitions within inversion substates ( b =0. 21 D) 0. 2 0 0 1 2 3 Frequency [THz] Calculated stick spectrum @ 75 K Ohio, International Symposium on Molecular Spectroscopy 4 Strong c-type transitions between inversion substates ( c =1. 47 D ) 22. 6. 2006 Christian Endres

ND 2 H Spectrum Asymmetric top = − 0. 2284 (prolate) 1 Intensity [ a. u. ] 0. 8 Inversion causes splitting into lower symmetric and upper asymmetric substates 0. 6 Each inversion doublet consists of one ortho- and one para- state 0. 4 Weak b-type transitions within inversion substates ( b =0. 21 D) 0. 2 0 0 1 2 3 Frequency [THz] Calculated stick spectrum @ 75 K Ohio, International Symposium on Molecular Spectroscopy 4 Strong c-type transitions between inversion substates ( c =1. 47 D ) 22. 6. 2006 Christian Endres

ND 2 H E [cm -1] a) E [cm -1] b) c) Spectrum Coriolis Interaction between closely spaced states with: J=0, Ka=0, Kc=± 1, and v=1 Especially strong perturbation if asymmetry splitting inversional splitting, like in case b) E [cm -1] Fig. : Ohio, International Symposium on Molecular Spectroscopy para ortho a) Inversion splitting > Asymmetry splitting b) Inversion splitting Asymmetry splitting c) Inversion splitting < Asymmetry splitting 22. 6. 2006 Christian Endres

Spectrometer in Cologne BWO Sideband BWO + Superlattice Multiplier 0 0. 5 1. 0 2. 5 3. 0 Frequency [THz] THz spectrometer (BWOs): Sideband spectrometer COSSTA: Multiplier spectrometer Ohio, International Symposium on Molecular Spectroscopy 0. 08 – 1. 2 THz 1. 75 – 2. 01 THz 0. 24 – 2. 7 THz 22. 6. 2006 Christian Endres

Spectrometer New Superlattice Setup PC 2 F Modulation Synthesizer 350 MHz PLL Lock-In 16 GHz IF Harmonic Mixer Lense Absorption cell Lense SL ~250 GHz Superlattice Multiplier (SL) 0. 75 - 2. 6 THz Bolometer Power Supply Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres

ND 2 H Measurements Partly resolved HFS for low rotational quanta J Largest contribution due to electric quadrupole interaction of 14 N Frequency [GHz] Spectrum measured with the 5 th harmonic of a BWO generated by the superlattice multiplier Ohio, International Symposium on Molecular Spectroscopy El. quadrupole interaction is considered in Ĥ and in fitting the line profile Line accuracy is checked by using closed cycles of transitions (Ritz-Combination-Principle) 22. 6. 2006 Christian Endres

ND 2 H Measurements from 0. 078 - 2. 578 THz Frequency uncertainty: mostly 10 -100 k. Hz partly - 500 k. Hz (>2 THz ) Frequency [THz] Radiation of the 11 th harmonic used to measure spectra up to 2. 58 THz Ohio, International Symposium on Molecular Spectroscopy 240 transitions in total (105 b-type, 135 c-type) 15 transitions involving strongly perturbed levels up to JKa. Kc= 138 5 , v = 0 22. 6. 2006 Christian Endres

ND 2 H Fit Hamiltonian Interaction Constants ( in MHz ) • S-reduced Hamiltonian F Ĥ = Ĥvv + Ĥ 01 + ĤHfs Ĥvv : terms up to 8 th order Ĥ 01 : terms up to 8 th order • 54 Parameters used in the fit Lines used in the fit # Lines RMS This work 240 0. 99 In total 923 0. 90 3129. 951(101) FK -9. 327(34) FJ 0. 8529(40) FKK 0. 02401(85) FJK x 103 0. 383(290) FJJ x 103 -1. 521(35) FKKK x 103 0. 03216(195) FJKK x 103 -0. 02250(102) FJJK x 106 -3. 090(84) FJJJ x 106 -0. 0949(105) Coriolis interaction between inversion substates substantially improved Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres

ND 2 H Predictions Frequency predictions up to 3 THz have been calculated using spcat → www. cdms. de Uncertainties of our predictions Up to J = 15 and Ka = 9 < 1 MHz For low lying rotational states, which are most important for astro. observations < 100 k. Hz (≈10 m/s at 3 THz) Endres et al. , J. Mol. Struct. , in press. 2006 Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres

Conclusion First successful application of the Superlattice Multiplier to record high resolution spectra with k. Hz accuracy up to THz frequencies. Reliable predictions of the inversion-rotation spectra of ND 2 H for astronomical observations up to 3 THz → www. cdms. de Ohio, International Symposium on Molecular Spectroscopy 22. 6. 2006 Christian Endres