ROTATIONAL SPECTRA OF THE N 2 OH + AND CH 2 CHCNH + MOLECULAR IONS Oscar Martinez Jr. Valerio Lattanzi Michael C. McCarthy Harvard-Smithsonian Center for Astrophysics School of Engineering and Applied Science, Harvard University Sven Thorwirth Max-Planck-Institut für Radioastronomie I. Physikalisches Institut, Universität zu Köln

Fourier-Transform Microwave Spectrometer Operating range: 5 to 42 GHz Pulsed nozzle (6Hz) supersonic molecular beam (~Mach 2) – 2.5 kTorr stagnation pressure behind nozzle, – Total flow 20 sccm – Results in T rot ~ 1 – 3 K – DC discharge used to create radicals and ions MW-MW double resonance capability effectively extends range to 60+ GHz McCarthy et al., ApJ Suppl. Ser. (2000)

Protonated Molecules Protonation plausibly occurs in our gas-phase hydrogen discharge via H 2 + H 2 + → H H H A → AH + + H 2 A number of protonated species studied by our group, including HNC 2 N +, HC 3 NH +, CH 3 CNH +, HSCO +, HSCS +, HSO 2 +, HNCOH +, and H 2 NCO + Interstellar weeds – Internal rotors e.g., methanol (CH 3 OH), methyl formate (HCOOCH 3 ), and dimethyl ether (CH 3 OCH 3 ) – and heavy species with no internal rotation e.g., propionitrile (CH 3 CH 2 CN) and acrylonitrile (CH 2 CHCN) – High density of spectral lines – Complicated spectra Can lead to misidentifications (e.g., glycine – NH 2 CH 2 COOH)

Protonated Nitrous Oxide (N 2 OH + and HN 2 O + isomers) N 2 O detected in ISM (Sgr B2) Ziurys et al., ApJ (1994) Theoretical work has examined structure Rice et al., Chem. Phys. Lett. (1986) Koichi and Mookuma, Chem. Phys. Lett. (1986) Martin and Lee, J. Chem Phys. (1993) Prior experimental work detected ground-state isomer (O-protonated) IR by Amano et al., Chem. Phys. Lett. (1986) and Jacox and Thompson, J. Chem. Phys. (2005) mm and sub-mm ( GHz) Bogey et al., Astron. Astrophys. (1986) and J. Chem. Phys. (1988) No prior detection of nitrogen hfs for O-protonated isomer No report of N-protonated isomer

HN 2 O + Experiment Computation: – Structure calculations at CCSD(T)/cc-pwCVQZ level of theory – Structure corrected for zero-point vibrational effects at CCSD(T)/cc-pVTZ level of theory Optimization on 1 0,1 → 0 0,0 transition of NNOH + McCarthy and Thaddeus J. Mol. Spec. (2010) – DC discharge (~1 kV) – 0.3% N 2 O heavily diluted in mixture of H 2 (10%) and He (90%) H O N N N N O H 4.35 kcal/mol (Martin and Lee, J. Chem Phys. 1993) E 4.05 kcal/mol (this work)

HN 2 O + 6 hyperfine-split lines detected in K a =0 ladder for N 2 OH + isomer 7 such lines detected for HN 2 O + isomer NNOH + HNNO + ConstantExperimentalPrevious*ExperimentalCalculated B eff (4) (12) (4) Χ aa (N outer )-3.330(4)…2.737(0)2.760 Χ aa (N inner )0.949(6)…-0.423(8) *Bogey et al. Phys. Rev. Lett. (1987) HN 2 O + N 2 OH +

Protonated Vinyl Cyanide (CH 2 CHCNH + ) Vinyl cyanide detected in ISM – Towards Sgr B2, in TMC-1 and in IRC st det by Gardner and Winnewisser, ApJ (1975) Dubbed an ‘interstellar weed’ Relatively high proton affinity of vc (784.7 kJ/mol, ~30% higher than CO) PVC essentially unreactive with many major interstellar constituents (e.g. H 2, CO, N 2, O 2 CH 4 and C 2 H 2 ) Petrie et al., MNRAS (1992) Relevant to planetary atmospheres PVC μ a =2.1 D Other protonated nitriles detected (HC 3 NH + and CH 3 CNH + ) Turner and Feldman, ApJ (1990)

PVC Experiment Search conditions first optimized on low-J line (2 0,2 → 1 0,1 transition at 22.5 GHz) of HSCO + McCarthy and Thaddeus, J. Chem. Phys. (2007) Search facilitated by computational support – Theoretical structure calculations at CCSD(T)/cc-pwCVQZ and corrected for zero-point vibrational effects – Theoretical rotational constants scaled by ratio of measured to calculated rate constants for vinyl acetylene (typically accurate to w/in 0.1%) Confirming lines found under optimized conditions for candidate (2 0,2 → 1 0,1 ) PVC line – 1.1 kV discharge – 40:1 flow ratio H 2 :1% vinyl cyanide in H 2

PVC 1 kV DC 1% VC 0.7 kV DC 1% VC 0.7 kV DC 0.1% VC

PVC MW-MW double resonance used to extend measurements to 46 GHz Lattanzi et al., J. Chem. Phys. (2010) – Enabled determination of line frequency for 5 0,5 → 4 0,4 transition 15 a-type rotational transitions – 8 from K a = 0 ladder – 7 from K a = 1 ladder Calculated ConstantExperimentalEquilibrium Vib. Contrib.Ground Vib. State A (69) B (11) C (74) μaμa 2.08 μbμb 0.47 Χ aa (69)0.286 Χ bb 0.325

Conclusion Rotational detection of HN 2 O + and measurement of hfs for both HN 2 O + and N 2 OH + Detection of protonated vinyl cyanide New cations are excellent candidates for radioastronomical detection Future targets: – Extend protonated VC data set into the mm-wave – Detection of other astronomically-relevant protonated species high proton affinity low reactivity with abundant neutrals high column density of neutral counterparts large dipole moments

Acknowledgements Harvard-Smithsonian Center for Astrophysics Funding Cambridge: NSF: CHE NASA: NNX08AE05G Cologne: Deutsche Forschungsgemeinschaft (TH1301/3-1)