Rotational Spectroscopy of the Lowest Energy Conformer of 2-Cyanobutane and Search for it in Sagittarius B2(N2) H. S. P. Müller, N. Wehres, O. Zingsheim, F. Lewen, S. Schlemmer, J.-U. Grabow, R. T. Garrod, A. Belloche, K. M. Menten 72nd ISMS, Urbana-Champaign, IL, 19 – 23 June 2017, MF03

Motivation ratio i-PrCN : n-PrCN: 0.40 ± 0.06 BuCN may be observable ALMA Cycles 0/1 survey at 3 mm toward Sgr B2(N), i-PrCN detected toward Sgr B2(N2); ratio i-PrCN : n-PrCN: 0.40 ± 0.06 A. Belloche et al., Science 345 (2014) 1584–1587 BuCN may be observable 4 isomers; rot. spectra of 2 known: n- & t-BuCN astrochemical modeling (Garrod et al., A&A 601 (2017) Art. No. A48): some reproduced i- to n- ratio & BuCN not much less than i-PrCN; branched 2-cyanobutane most abundant isomer, n-BuCN and 3-methylbutyronitrile slightly less, t-BuCN almost negligible Spectra of 2-cyanobutane and 3-methylbutyronitrile taken

Conformers of 2-Cyanobutane CN CH3 H 2-cyano-anti-butane (2-methyl-gauche'-butyronitrile) ΔE = 0 cm−1 H3C 2-cyano-gauche-butane (2-methyl-anti-butyronitrile) ~249 cm−1 2-cyano-gauche'-butane (2-methyl-gauche-butyronitrile) ~283 cm−1 Energies from molecular mechanics calculations (+ IR & Ra + FF): G. A. Crowder & G. O. Carlisle, J. Comp. Chem. 12 (1991) 880

Model of 2-Cyano-anti-butane

Recorded Spectra in Hannover chirped pulse FTMW measurements with jet expansion (Trot a few K) 1 GHz wide scans around 14.9, 15.9, 16.7, 17.0, and 22.7 GHz cavity FTMW measurements with jet expansion (Trot a few K) 2 − 24 GHz near lines of anti conformer (~ 1 MHz wide scans)

Chirped Pulse FTMW Spectrum calculated stick spectrum @ 3 K ≤ 26.5 GHz b-, a-, a-, b-type; Kc" = J" = 3, Ka = 0, 1

Rotational and Quartic Distortion Parameters Exptl. B3LYP MP2 MP3 A (MHz) 4070 .37 4104 .35 4073 .64 4097 .39 B (MHz) 3145 .92 3093 .05 3184 .78 3148 .54 C (MHz) 1919 .40 196 .51 1935 .93 1927 .03 DK (kHz) 1 .942 .831 2 .015   DJK (kHz) ­−4 .280 .097 .422 DJ (kHz) .572 .495 .649 d1 (Hz) −37 .26 15 −83 .52 d2 (Hz) −561 .4 −569 .2 −604 .5 κ .1404 .0797 .1684 .1256 κ = (2B – A – C)/(A – C) μa: 2.3 D, μb: 3.3 D, μc: 0.6 D

The 110 − 101 Transition with HFS

14N Nuclear Quadrupole Coupling Parameters Exptl. B3LYP MP2 MP3//MP2 MP3 χaa 0.296 0.201 0.269 0.288 0.257 χbb −2.144 −2.270 −1.957 −2.181 −2.272 χcc 1.849 2.069 1.688 1.893 2.015 χab 2.90 3.145 2.559 2.840 3.052 basis set: aug-cc-pVTZ; except MP3: cc-pVTZ

Recorded Spectra in Köln and Overview of Results 2 x 7 m long double path glass cells; RT (heated); Schottky diode detector ► 36.0 − 47.7 & 52.0 − 65.0 GHz: synthesizer J ≤ 87, Ka ≤ 47; R, Q; (HFS) ► 90 − 126 GHz: synthesizer + tripler (VDI) J ≤ 100, Ka ≤ 56; R, Q 5 m long double path glass cells; RT (heated); Schottky diode detector 18 = 3, Verstärker, 3, 2 36 = 3, Verstärker, 3, 2, 2 ► 175 − 200 GHz: synthesizer + multiplier (x18; VDI) J ≤ 11, Ka ≤ 73; R, Q ► 360 − 401 GHz: synthesizer + multiplier (x36; VDI) J ≤ 104, Ka ≤ 68; R

Detail of the Millimeter Wave Spectrum of 2-Cyanobutane

Search for 2-Cyanobutane in Sgr B2(N2) ALMA Cycle 0 and 1 survey of Sgr B2(N) at 3 mm (84.0 − 114.4 GHz) Exploring Molecular Complexity with ALMA (EMoCA) previous talk and Belloche et al., A&A 587 (2016) Art. No. A91 Assuming Trot = 150 K and a source size of 1", as for i- and n-PrCN (Belloche et al., Science 345 (2014) 1584–1587): i-PrCN : 2-CAB > 6 & n-PrCN : 2-CAB > 16

Conclusion and Outlook Ground vibrational state of lowest conformer of 2-cyanobutane characterized Lines identified for v39 = 1 and for 2nd lowest conformer Ground vib. states of two conformers of 3-methylbutyronitrile almost done Search for 3rd conformer of 2-cyanobutane (+ vib. states) continues 2-Cyanobutane and other BuCN isomers may be found in new ALMA data; higher sensitivity and higher spatial resolution observations partially taken in Cycle 4

Acknowledgments Marius Hermanns (help during measurements in Hannover) Support by Deutsche Forschungsgemeinschaft (DFG) via collaborative research grant SFB 956 "Conditions and Impact of Star Formation", project area B3 OZ is grateful for a stipend from the Bonn-Cologne Graduate School of Physics and Astronomy (BCGS)

The Star-forming Region Sagittarius B2 most massive star-forming region in our Galaxy (~ 107 M) ~100 pc from Galactic Center 2 massive clumps, (M) and (N), hosting clusters of UC HII regions Central Molecular Zone at 870 µm ATLASGAL/LABOCA & Planck; © MPIfR/A. Weiß Sgr B2(N) Sgr B2(N) at 850 µm (SMA; Qin et al., 2011) 2 hot cores: N1 (or LMH) & N2 different vlsr (10 km/s); 5" apart (0.2 pc) many COMs first detected there very high column densities (> 1025 cm–2) key for detection of COMs

Exploring Molecular Complexity with ALMA 3 mm spectral line survey of Sgr B2(N) in Cycles 0 and 1 (84.0 – 114.4 GHz) angular resolution: 1.6" (median) ~ 12 % der Linien > 3 K sind U; zu vermuten: hauptsächlich höhere Zustände von EtCN und VyCN. sensitivity to compact emission: factor ~20 compared to our IRAM 30 m survey status: analysis ongoing; published: detection of i-PrCN (Science, 2014); deuterated COMs, ROH & RSH, C2H5CN with 2 13C (all A&A, 2016)