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 560012 India. bIndian Institute of Science Education and Research, Pashan, Pune, Maharashtra 411008 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

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!!” http://phys.org/news/2014-6-familiar-strange-personality-revealed.html http://en.wikipedia.org/wiki/Sphere_packing E. Arunan and D. Mani, Faraday Discuss.,2015, 177, 51 E. Arunan UCI-CaSTL Centre talk 22 January 2016 .

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)

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

A Look Back to 1988: 43rd ISMS Observed Transitions for H32SH···32SH2 (E1 State) J K-1 K+1 Frequency (MHz) Residue 1 0 1 0 0 0 3498.561(4) 3 2 0 2 6996.761(4) 3 0 3 10494.240(4) -1 4 0 4 13990.645(4) -3 5 0 5 17485.615(8) -7 6 0 6 20978.803(4) 1 Fitted Constants(E1 State) (B+C)/2 /MHz 1752.8815(12) DJ /kHz 15.081(36) F. J Lovas, P. K Mandal and E. Arunan, unpublished work P. K. Mandal, Ph.D. Dissertation, Indian Institute of Science, (2005) F. J. Lovas, R. D. Suenram, and L. H. Coudert, 43rd Int.Symp.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)

Observed Transitions for H32SH···32SH2 (E2 State) J K-1 K+1 Frequency (MHz) Residue 1 0 1 0 0 0 3496.141(4) 4 2 0 2 6991.949(4) 1 3 0 3 10487.005(4) -2 4 0 4 13980.969(4) -1 5 0 5 17473.460(8) -6 6 0 6 20964.135(4) Fitted Constants (E2 State) (B+C)/2 /MHz 1752.8815(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)

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

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

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.

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

Observed Transitions for H32SH···32SH2 (E1 State) J K-1 K+1 Frequency (MHz) Residue 1 0 1 0 0 0 3498.5605 0.0025 2 1 2 1 1 1 6991.7730 0.0060 2 0 2 6996.7610 0.0036 2 1 1 1 1 0 7006.0220 0.0062 3 1 3 10486.7555 0.0017 3 0 3 10494.2400 -0.0025 3 1 2 10508.0710 0.0027 4 1 4 13980.6620 -0.0026 4 0 4 13990.6459 -0.0009 4 1 3 14008.9690 -0.0055 5 1 5 17473.1350 -0.0057 5 0 5 17485.6150 -0.0047 5 1 4 17508.3490 -0.0031 6 1 6 20963.8270 6 0 6 20978.8031 0.0028 6 1 5 21005.8220 0.0029 Blue colored lines are K=1 lines

Fitted Constants B /MHz 1752.8788(11) C /MHz 1745.7388(11) DJ /kHz H32SH···32SH2 (E1 State) B /MHz 1752.8788(11) C /MHz 1745.7388(11) DJ /kHz 14.921(11) DJK /kHz -537.46(80) d1 /kHz -0.4886(86) HJK /Hz -508.(14) s /kHz 4.8 # transitions 16 Ab-initio value (97293.25MHz) of the A rotational constant has been used for fitting.

Observed Transitions for H32SH···32SH2 (E2 State) J K-1 K+1 Frequency (MHz) Residue 1 0 1 0 0 0 3496.1609 0.0035 2 1 2 1 1 1 6985.1597 -0.0010 2 0 2 6991.9510 0.0024 2 1 1 1 1 0 7001.7420 -0.0003 3 1 3 10479.2300 0.0001 3 0 3 10487.0080 -0.0004 3 1 2 10499.2550 -0.2342(e) 4 0 4 13990.6459 -0.0023 4 1 3 13995.6420 0.0003 5 1 5 4 1 4 17462.5527 -0.0001 5 0 5 17473.4680 -0.0025 5 1 4 17493.2586 6 0 6 20964.1353 0.0018 Blue colored lines are K=1 lines (e): excluded from fit

Fitted Constants B /MHz 1753.1004(79) C /MHz 1743.1178(79) DJ /kHz H32SH···32SH2 (E2 State) B /MHz 1753.1004(79) C /MHz 1743.1178(79) DJ /kHz 15.2281(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 (97293.25MHz) of the A rotational constant has been used for fitting.

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 49142.17 58761.68 49176.69 B /MHz 1676.83 1709.19 1679.95 C /MHz 1662.42 1690.05 1665.52 Optimizations are performed at MP2/aug-cc-pVDZ

Observed Transitions for DSD···SD2 E1 State E2 State J K-1 K+1 Frequency (MHz) Residue 1 0 1 0 0 0 3290.5189 -0.0152 2 1 2 1 1 1 6575.6901 -0.0022 2 0 2 6580.7398 0.0011 2 1 1 1 1 0 6587.1789 -0.0141 3 1 3 9862.5498 -0.0025 3 0 3 9870.3021 0.0092 3 1 2 9879.8857 0.0044 4 1 4 13148.2420 0.0008 4 0 4 13158.8634 0.0004 4 1 3 13171.4835 0.0036 5 0 5 16446.1203 -0.0032 5 1 4 16461.6300 0.0047 6 0 6 19731.7480 0.0007 6 1 5 19749.9505 -0.0038 J K-1 K+1 Frequency (MHz) Residue 1 0 1 0 0 0 3288.7550 -0.0099 2 1 2 1 1 1 6572.8510 -0.0135 2 0 2 6577.2150 0.0077 2 1 1 1 1 0 6582.6610 0.0006 3 0 3 9865.0070 0.0021 3 1 2 9873.2519 0.0047 4 1 4 3 1 3 13144.2565 0.0159 4 0 4 13151.8330 -0.0024 4 1 3 13162.9395 5 1 5 16428.8980 -0.0073 5 0 5 16437.3740 -0.0023 5 1 4 16451.4430 -0.0043 6 0 6 19721.3070 0.0015 6 1 5 19738.4685 0.0026 Blue colored lines are K=1 lines

Fitted Constants B /MHz 1648.1610(28) 1646.895(16) C /MHz DSD ··· SD2(E1 State) DSD··· SD2(E2 State) B /MHz 1648.1610(28) 1646.895(16) C /MHz 1642.4275(28) 1641.923(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 .

Observed signals for HSD···SD2 J K-1 K+1 Frequency (MHz) Residue 1 0 1 0 0 0 3357.4490 0.0045 2 0 2 6714.5770 0.0019 2 1 1 1 1 0 6722.0485 -0.0027 3 1 3 2 1 2 10065.7175 -0.0038 3 0 3 10071.0780 0.0000 3 1 2 10082.3848 0.0033 4 1 4 13419.5205 0.0024 4 0 4 13426.6380 -0.0013 5 1 5 16772.0794 0.0021 5 0 5 16780.9420 -0.0031 5 1 4 4 1 3 16800.2589 -0.0017 6 1 6 20123.0882 -0.0015 6 0 6 20133.6835 6 1 5 20157.2538 0.0007 Fitted Constants B /MHz 1681.50165(87) C /MHz 1675.99511(87) DJ /kHz 13.0673(81) DJK /kHz -480.48(58) d1 /kHz 0.6505(65) HJK /Hz 830.(10) s/kHz 3.3 # transitions 14 Blue colored lines are K=1 lines

Observed signals for DSD···SDH J K-1 K+1 Frequency (MHz) Residue 1 0 1 0 0 0 3355.9220 -0.0045 2 1 2 1 1 1 6708.2098 -0.0175 2 0 2 6711.5490 0.0048 2 1 1 1 1 0 6716.3067 -0.0017 3 1 3 10061.5800 0.0023 3 0 3 10066.5440 -0.0004 3 1 2 10074.2004 0.0188 4 1 4 13414.0216 0.0094 4 0 4 13420.6170 -0.0011 4 1 3 13431.6998 -0.0178 5 1 5 16765.2286 0.0032 5 0 5 16773.4560 -0.0005 6 1 6 20114.9078 -0.0043 6 0 6 20124.7510 0.0005 6 1 5 5 1 4 20145.3311 0.0030 Fitted Constants B /MHz 1679.9449(60) C /MHz 1676.0329(60) DJ /kHz 12.8595(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

New Progression of Lines J K-1 K+1 Frequency (MHz) Residue 1 0 1 0 0 0 3511.474 -0.001 2 0 2 7022.566 0.008 3 0 3 10532.870 0.010 4 0 4 14041.986 0.003 5 0 5 17549.561 0.007 6 0 6 21055.177 0.013 Fitted Constants (B+C)/2 /MHz 1755.770 DJ /kHz 16.3 s/kHz 7.4 The new progression looks like it belongs to the parent isotopologue.

Summary H32SH···32SH2 (E1) H32SH···32SH2 (E2) D 32SD···32SD2 (E1) H32SD···32S D2 (A1) D32SD···32SDH B /MHz 1752.8788(11) 1753.1004(79) 1648.1610(28) 1646.895(16) 1681.50165(87) 1679.9449(60) C /MHz 1745.7388(11) 1743.1178(79) 1642.4275(28) 1641.923(16) 1675.99511(87) 1676.0329(60) DJ /kHz 14.921(11) 15.2281(66) 13.628(21) 13.426(11) 13.0673(81) 12.8595(59) DJK /kHz -537.46(80) -362.7(16) -192.6(17) -111.8(81) -480.48(58) -147.5(30) d1 /kHz -0.4886(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

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(404 -303) Probable Transitions(606-505) 13966.61 21001.31 13966.7 21001.28 13966.99 21004.35 13966.85 21004.37 13967.109 21006.0 13967.2 21006.1

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.

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

for your kind attention Thank you for your kind attention Picture taken from: http://www.iisc.ac.in/