Rotational spectroscopy of thioformaldehyde, H2CS,in its four lowest excited vibrational, Coriolis-coupled states

Holger S. P. Müller, C. P. Endres, S. SchlemmerA. Maeda, I. Medvedev, E. Herbst, M. Winnewisser, F. C. De Lucia

62nd International Symposium on Molecular Spectroscopy; WG04

Motivation

• important molecule in interstellar medium

• textbook example for Coriolis interaction

v = 0

v3 = δs(CH2)

v2 = v(CS)

v1 = vs(CH2) v5 = vas(CH2)

v6 = ρ(CH2)v4 = oop1455.496

1059.205990.185 991.019

2971.03 3024.62

A1 B1 B2

Previous Work

• v = 0: presentation TI08 by Atsuko Maeda et al.

• v3, v4, v6 laser Stark spectroscopy: Bedwell & Duxbury, JMSp 84 (1980) 531 est. err.: 0.001 cm−1, some larger residuals

• v3, v4, v6 FTIR spectroscopy: P. H. Turner et al., JMSp 88 (1981) 402 est. err.: 0.010 cm−1, some larger residuals

• v2 FTIR spectroscopy: McNaughton & Bruget, JMSp 159 (1993) 340 est. err.: 0.0005 cm−1, 84 lines with larger residuals omitted

• also: v3, v4, v6 FTIR spectroscopy by W. J. Lafferty et al. (TC07)

Current Work

pyrolysis of c-C3H6S (trimethylene sulfide) → H2CS

OSU: FASSST (BWOs) 120 − 380 GHz ≡ J” = 3 – 9• complete & fast coverage• typical uncertainty: 100 kHz (used throughout)

Uni Köln: Cologne THz Spectrometer 574 − 670 GHz ≡ J” = 17, 18• phase-locked BWOs

• typical uncertainty: ~ 10 kHz (here: 5 − 50 kHz)

• selected transitions (~ 2J complete)• slower; high sensitivity

J = Ka energy levels I

E (cm−1)

2000

1500

1000

5

10

v4 = 1

5

10

v6 = 1

no Coriolis interaction

10

v6 = 1v4 = 1

5

with Coriolis interaction

intensity effects

asymmetry splitting in Ka = 4 I

1.31 MHz

asymmetry splitting in Ka = 4 II

anomalousK-splitting

−1.29 MHz

J = Ka energy levels II

E (cm−1)

2000

1500

1000

10

v6 = 1v4 = 1

55

2

8

5

10

v3 = 1

a weak line

J = Ka energy levels III

E (cm−1)

2000

1500

1000

10

v6 = 1v4 = 1

55

2

8

5

10

v3 = 1 v2 = 1

5

10

asymmetry splitting in Ka = 4 III

1.79 MHz

The Current Dataset*

• 27 misc. v = 0 MW and mmW lines

• 358 FIR v = 0 lines (McNaughton & Bruget)

• 372 (sub-) mmW lines from OSU

• 144 sub-mmW lines from Köln

• 76 − 10 ν3, ν4, ν6 lines from Bedwell & Duxbury

• 127 − 10 ν3, ν4, ν6 lines from Turner et al.

• 436 − 6 ν2 lines from McNaughton & Bruget

*) unresolved asymmetry splitting counted only once

Interaction Terms

iGaJa + iGaJ{Ja, J2} + iGaKJa3 + iG2a{Ja, J+

2 + J−2} + . . .

+Fbc{Jb,Jc} + . . .

A Satifactory Model

• S-reduction; 17 parameter for v = 0 (B, D, H + 2; 2 fixed)

• E + 4 to 6 × ΔX for each vi = 1

• 5 Gijg from own ab initio calc. (MP2/cc-pCVQZ); 3 released

• 0 – 7 distortion terms for each Gijg

rms error of 1.0

Spectroscopic Parameters (cm−1, MHz) of H2CS(or Differences)

v = 0 v4 = 1 v6 = 1 v3 = 1 v2 = 1

E 990.183 991.021 1059.205 1455.496

(Δ) A − (B + C)/2l 274439. − 476. −221. 2510.

(Δ) (B + C)/2 17175.747 −2.92 −11.70 −107.19 −27.39

(Δ) (B − C)/4 261.6240 −5.32 12.46 −1.26 6.73

(Δ) DK 23.7 − − − 2.05

(Δ) DJK × 10−3 522.3 −0.04 1.5 18.1

(Δ) DJ × 10−3 19.02 0.16 0.13 0.17 −0.10

+ 1 × Δd1 + 2 × ΔHKJ

Interaction Parameters (MHz)

X46a X24

b X34b X36

c

Gi 300219. 30846. 2032. 9140. GiK −59.3 7.1 0.109 −1.3 GiJ −0.819 −0.06 − −0.044 G2i 1.02 0.040 − 0.015