Submillimeter-wave Spectroscopy of Thioformaldehyde, H2CS, in its Ground State Atusko Maeda, Ivan Medvedev, Eric Herbst, Mandfred Winnewisser, Frank C. De Lucia , Department of Physics, The Ohio State University, Columbus, OH 43210, USA; Holger S. P. Müller, Christian P. Endres & Stephan Schlemmer I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.

Thioformaldehyde, H2CS a Planar asymmetric molecule Asymmetry parameter κ = –0.99 a Dipole moment along a-axis: μa = 1.6483 Debye (Fabricant et al. 1977) a-type transitions (ΔKa = 0, ±2…, ΔKc = ±1, ±3…)

Previous Spectroscopic Studies Rotational spectroscopy * H2CS, microwave(1) * H2CS, D2CS, H213CS, H2C34S, microwave in 1-70 GHz(2) * H2CS, millimeter-wave in 104-244 GHz(3) * H2C33S, microwave in 1-37 GHz(4) * H2CS, H2C34S, FIR in 16-60 cm-1(5) * HDCS, millimeter-wave in 90-400 GHz(6) J = 27, Ka = 0-2 J = 53, Ka = 0-9 (1) Johnson & Powell 1970, (2) Johnson, Powell & Kirchhoff 1971, (3) Beers et al. 1972, (4) Brown et al. 1987, (5) Mc Naughton & Bruget 1993 (6) Minowa et al. 1997

S-bearing Molecules in the Interstellar (H2S, SO, SO2, OCS, H2CS…) O,B star S-compounds S Ultra-compact HII region Heated up! H2S? OCS? grain mantle T = 100-300 K n = 106-108 cm-3 H2CS abundance can be chemical clock → Age of heated gas Cold background

Odin Observation toward Orion KL Old Prediction extrapolated from low freq. data Transition Odin J' Ka' Kc' J'' Ka'' Kc'' Obs. Freq. (MHz) 14 1 13 12 487663 16 15 547315 2 548927 4 549201 11 3 549407 549452 6.3 15.3 16.6 16.8 16.4 12.2 11.9 Obs.(Odin)-Pred.(old) Laboratory measurement at higher frequency!! (at least better prediction…)

Experimental Conditions FASSST Spectrometer @ OSU 120-370 GHz with 3 BWOs 100 scans accumulation up- & down-ward scans averaged SO2 for frequency calibration better than 100 kHz uncertainty Terahertz Spectrometer @ U. Cologne 570-670 GHz with a BWO Phase-lock-loop (PLL) technique → frequency stabilization ~5 kHz experimental uncertainty higher frequencies intended…. Production of H2CS Pyrolysis of trimethylene-sulfide [(CH2)3S] (Sigma-Aldrich Co.) at 680 ℃ (at OSU), 1300 ℃ (at Cologne)

Spectrum Assignment Predictions with SPFIT/SPCAT(1) program suites based on previous microwave & millimeter-wave (& FIR) transitions of H2CS, H2C34S, H2C33S, H213CS. CAAARS(2) (Computer Aided Assignment of Asymmetric Rotor Spectra) program for the FASSST spectrum Pickett, J. Mol. Spectrosc., 148, 371 (1991), http://spec.jpl/nasa.gov Medvedev et al. J. Mol. Struct. 742, 229 (2005)

Intensities agree with natural abundance ratio FASSST Spectrum of H2CS 85,4←75,3 85,3←75,2 H2CS 80,8←70,7 H2C34S ×10 Intensities agree with natural abundance ratio 32S : 33S : 34S = 95 : 0.75 : 4.2 12C : 13C = 99 : 1 H2C33S H213CS ×100 ×100

Terahertz Spectrum of H2CS 1913,6←1813,5 1913,7←1813,6 R-branch (ΔJ = +1) ΔK = 0 P-branch (ΔJ = –1) ΔK = 2

Summary of Transitions Newly Assigned Previous data + Microwave + FIR transitions H2CS (200 transitions) a-type R: J=3-18, Ka=0-15, Q: J=15-44, Ka=1-2 P: J=13,14, Ka=0. H2C34S (140 transitions) a-type R: J=3-19, Ka=0-11, Q: J=15-26, Ka=1. H2C33S (360 transitions) with I=3/2 a-type R: J=3-19, Ka=0-11, Q: J=16-19, Ka=1. H213CS (150 transitions) a-type R: J=3-19, Ka=0-11, Q: J=16-23, Ka=1. Ka up to 15! Ka up to 11!

Analysis with SPFIT Effective rotational Hamiltonian for asymmetric-top molecules in Watson’s S-reduced form HR = AJa2 + BJb2 + CJc2 – DJJ4 – DJKJ2Ja2 – DKJa4 + d1J2[(J+)2 + (J–)2] + d2[(J+)4 + (J–)4] + (higher order centrifugal distortion terms) * For 33S species with I = 3/2, Hyperfine interaction Hamiltonian is added Hhyp = HeQq + HRI

New transition frequency predictions Molecular Constants New transition frequency predictions for 4 isotopic species!

Frequency Comparison [MHz] between Odin & New Prediction Transition Odin New Prediction Residuals J' Ka' Kc' J'' Ka'' Kc'' Obs. Freq. Calc. Freq. 14 1 13 12 487663 487663.321 –0.3 16 15 547315 547307.994 7.0 2 548927 548920.315 6.7 4 549201 549188.338 12.7 11 549188.727 12.3 3 549407 549402.035 5.0 549452 549447.188 4.8

Line Surveys of Orion-KL by Schilke et al. 1) 325-365 GHz (1997) Frequency Comparison [MHz] Extrapolated from low frequency data

Line Surveys of Orion-KL by Schilke et al. 2) 607-725 GHz (2001) Extrapolated from low frequency data

The Equilibrium Structure of H2CS

Conclusion Rotational spectra of thioformaldehyde in the ground state were observed for 4 isotopic species; H2CS, H2C34S, H2C33S, H213CS. Discrepancies between new lab. measurements and old predictions at high Ka(≥4) were found at most 3 MHz in the FASSST spectrum. Intensity ratios of lines of isotopic species agree with natural abundance ratio, supporting the isotopic assignments. R-branch transitions with J ≤ 19 & Ka ≤ 15, Q-branch transitions with J ≤ 44 & Ka ≤ 2 have been assigned. New predictions/measurements allow unambiguous identification of interstellar lines. Precise equilibrium molecular structure of H2CS is determined. Satellite band spectra were found and assigned to ν2, ν3, ν4, and ν6 Global analysis →→→→→ WG04 (Microwave session)