1. Rotational Spectra of H2S Dimer: Observation of Ka =1 Lines
Arijit Dasa, Pankaj Mandalb, Frank J. Lovasc, Chris Medcraftd, and E. Arunana
aDepartment of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore India.
bIndian Institute of Science Education and Research, Pashan, Pune, Maharashtra
cNational Institute of Standards and Technology, Optical Sensors Division,100 Bureau Dr.,Gaithersburg, MD 20899
dSchool of Chemistry,Newcastle University,Bedson Building,Newcastle upon Tyne,Tyne and Wear NE1 7RU,United Kingdom

2. H2O vs. H2S in Condensed Phase
Hydrogen bonding
van der Waals interaction
H2O at 0 °C 4 neighbours
H2S at – 60 °C 12 neighbours
“They were as different as apples and oranges!!”
E. Arunan and D. Mani, Faraday Discuss.,2015, 177, 51
E. Arunan UCI-CaSTL Centre talk 22 January

3. Hydrogen Bonding and van der Waals Interaction
In Pauling’s classic book of “THE NATURE OF THE CHEMICAL BOND” there is a chapter on hydrogen bond.
(L. Pauling, The Nature of the Chemical Bond, Cornell University Press, 1939.)
Hydrogen bonding : Simple dipole-dipole interaction?
Physical forces behind hydrogen bonding and van der Waals interaction are very similar.(E. Arunan and D. Mani, Faraday Discuss., 2015, 177, 51)
All intermolecular interactions, including hydrogen bonding, should be classified as van der Waals interactions.(E. Arunan, written for ISRAPS Bulletin (2005)

4. H2O Dimer and H2S Dimer in Optimized Geometry
Optimized geometry of the H2O dimer & H2S dimer, look very similar
E. Arunan and D. Mani, Faraday Discuss.,2015,177, 51
Electron Density Topology
Both are Hydrogen Bonded!!
Bond Critical Point

5. A Look Back to 1988: 43rd ISMS
Observed Transitions for H32SH···32SH2 (E1 State)
J K-1 K+1
Frequency
(MHz)
Residue
(4) 3
(4)
(4) -1
(4) -3
(8) -7
(4) 1
Fitted Constants(E1 State)
(B+C)/2 /MHz
(12)
DJ /kHz
15.081(36)
F. J Lovas, P. K Mandal and E. Arunan, unpublished work
P. K. Mandal, Ph.D. Dissertation, Indian Institute of Science, (2005)
F. J. Lovas, R. D. Suenram, and L. H. Coudert, 43rd Int.Symp. on Molecular Spectroscopy. (1988)

6. Observed Transitions for H32SH···32SH2 (E2 State)
J K-1 K+1
Frequency
(MHz)
Residue
(4) 4
(4) 1
(4) -2
(4) -1
(8) -6
(4)
Fitted Constants (E2 State)
(B+C)/2 /MHz
(12)
DJ /kHz
15.081(36)
K=0 lines for H34SH···32SH2 , H32SH···34SH2, D32SH···32SDH, H32SD···32SD2, H34SD···32SD2, H32SD···32SD2, D32SD···32SD2, D34SD···32SD2 were also known.
H232S ···34SH2(Lower State), H234S ···32SH2(Lower State), H2 S/D2S/HDS K=0 transitions had been found by Dr. Pankaj Kanti Mandal.
F. J Lovas, P. K Mandal and E. Arunan, unpublished work
P. K. Mandal, Ph.D. Dissertation, Indian Institute of Science, (2005)
F. J. Lovas, R. D. Suenram, and L. H. Coudert, 43rd Int.Symp. on Molecular Spectroscopy. (1988)

7. Structure of Hydrogen Sulphide Dimer Derived from K=0 Lines
4.116(4)Å
Fitting the K=0 lines, only the distance between two sulphur atoms can be obtained.
Absence of K=1 lines indicates, the interaction between two H2S molecules is isotropic.
That means the structure still looks like two oranges!!! (average ‘spherical shape’)
H2S Dimer : Hydrogen Bonded or van der Waals interaction???
F. J Lovas, P. K Mandal and E. Arunan, unpublished work
E. Arunan and D. Mani, Faraday Discuss., 2015, 177, 51

8. Symmetric/Asymmetric top
C6H6···H2O
Theory
Experiment
Asymmetric top
Symmetric top
Water has little or no barrier to internal rotation about six fold axis of benzene.
K=1 lines absent
K=1 lines present
Diatomic Rotor
Symmetric/Asymmetric top
Since the intermolecular potential energy surface is expected to be shallow. The hydrogen atoms in the H2S dimer may not have any specific orientations.
H. S. Gutowsky, T. Emilsson and E. Arunan, J. Chem. Phys., 99, 4883 (1993)
F. J Lovas, P. K Mandal and E. Arunan, unpublished work

9. K=1 Lines observed for H2S Dimer
When Dr. Chris Medcraft mentioned about the possibilities of observing K=1 lines for HDS ···H2S, we started looking again.

10. K=1 Lines observed for H2S Dimer
We have finally found out the K=1 lines for parent isotopologue.

11. Observed Transitions for H32SH···32SH2 (E1 State)
J K-1 K+1
Frequency
(MHz)
Residue
0.0025
0.0060
0.0036
0.0062
0.0017
0.0027
0.0028
0.0029
Blue colored lines are K=1 lines

12. Fitted Constants B /MHz 1752.8788(11) C /MHz 1745.7388(11) DJ /kHz
H32SH···32SH2 (E1 State)
B /MHz
(11)
C /MHz
(11)
DJ /kHz
14.921(11)
DJK /kHz
(80)
d1 /kHz
(86)
HJK /Hz
-508.(14)
s /kHz
4.8
# transitions 16
Ab-initio value ( MHz) of the A rotational constant has been used for fitting.

13. Observed Transitions for H32SH···32SH2 (E2 State)
J K-1 K+1
Frequency
(MHz)
Residue
0.0035
0.0024
0.0001
(e)
0.0003
0.0018
Blue colored lines are K=1 lines
(e): excluded from fit

14. Fitted Constants B /MHz 1753.1004(79) C /MHz 1743.1178(79) DJ /kHz
H32SH···32SH2 (E2 State)
B /MHz
(79)
C /MHz
(79)
DJ /kHz
(66)
DJK /kHz
-362.7(16)
d1 /kHz
-59.81(28)
HJK /Hz
1605.(42)
h1/Hz
1068.6(56)
s/kHz
2.6
# transitions 13
Ab-initio value ( MHz) of the A rotational constant has been used for fitting.

15. Calculated Constants of Isotopologues
DSD···SD2
HSD···SD2
DSD···SDH D H D H D D
Calculated Rotational Constants
DSD···SD2
HSD···SD2
DSD···SDH
A /MHz
B /MHz
C /MHz
Optimizations are performed at MP2/aug-cc-pVDZ

16. Observed Transitions for DSD···SD2
E1 State
E2 State
J K-1 K+1
Frequency
(MHz)
Residue
0.0011
0.0092
0.0044
0.0008
0.0004
0.0036
0.0047
0.0007
J K-1 K+1
Frequency
(MHz)
Residue
0.0077
0.0006
0.0021
0.0047
0.0159
0.0015
0.0026
Blue colored lines are K=1 lines

17. Fitted Constants B /MHz 1648.1610(28) 1646.895(16) C /MHz
DSD ··· SD2(E1 State)
DSD··· SD2(E2 State)
B /MHz
(28)
(16)
C /MHz
(28)
(16)
DJ /kHz
13.628(21)
13.426(11)
DJK /kHz
-192.6(17)
-111.8(81)
d1 /kHz
-0.594(46)
-2.31(18)
HJK /Hz
-2100.(50)
3357.(184)
s/kHz
8.7
9.4
# transitions 14 .

18. Observed signals for HSD···SD2
J K-1 K+1
Frequency
(MHz)
Residue
0.0045
0.0019
0.0000
0.0033
0.0024
0.0021
0.0007
Fitted Constants
B /MHz
(87)
C /MHz
(87)
DJ /kHz
(81)
DJK /kHz
(58)
d1 /kHz
0.6505(65)
HJK /Hz
830.(10)
s/kHz
3.3
# transitions 14
Blue colored lines are K=1 lines

19. Observed signals for DSD···SDH
J K-1 K+1
Frequency
(MHz)
Residue
0.0048
0.0023
0.0188
0.0094
0.0032
0.0005
0.0030
Fitted Constants
B /MHz
(60)
C /MHz
(60)
DJ /kHz
(59)
DJK /kHz
-147.5(30)
d1 /kHz
4.018(54)
HJK /Hz
4159.(54)
s/kHz
11.3
# transitions 15
Blue colored lines are K=1 lines

20. New Progression of Lines
J K-1 K+1
Frequency
(MHz)
Residue
-0.001
0.008
0.010
0.003
0.007
0.013
Fitted Constants
(B+C)/2 /MHz
DJ /kHz
16.3
s/kHz
7.4
The new progression looks like it belongs to the parent isotopologue.

21. Summary H32SH···32SH2 (E1) H32SH···32SH2 (E2) D 32SD···32SD2 (E1)
H32SD···32S D2
(A1)
D32SD···32SDH
B /MHz
(11)
(79)
(28)
(16)
(87)
(60)
C /MHz
(11)
(79)
(28)
(16)
(87)
(60)
DJ /kHz
14.921(11)
(66)
13.628(21)
13.426(11)
(81)
(59)
DJK /kHz
(80)
-362.7(16)
-192.6(17)
-111.8(81)
(58)
-147.5(30)
d1 /kHz
(86)
-59.81(28)
-0.594(46)
-2.31(18)
0.6505(65)
4.018(54)
HJK /Hz
-508.(14)
1605.(42)
-2100.(50)
3357.(184)
830.(10)
4159.(54)
h1/Hz
-----
1068.6(56)
s/kHz
4.8
2.6
8.7
9.4
3.3
11.3
#transitions 16 13 14 15

22. Probable 33S transitions
Hyperfine structure from the 33S quadrupole interaction, observed with Doppler doubling in the J=4–3 transitions(a part of the spectra) for H2S···H233S/ H233S···H2S.
Probable Transitions( )
Probable Transitions( )

23. Conclusions
K=1 lines for H32SH···32SH2 /D 32SD···32SD2 /H32SD···32S D2/D32SD···32SDH have been identified and assigned.
The natural abundance(0.76%) of 33S is large enough to enable us to observe the transitions of H2S···H233S/ H233S···H2S.
The presence of K=1 lines prove that H2S dimer structure has hydrogen bond and the interaction is not isotropic.

24. Acknowledgments
Indian Institute of Science, Bangalore, India for financial support for this trip.
Department of Science and Technology(DST), India for funding.

25. for your kind attention
Thank you
for your kind attention
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