FT Microwave and MMW Spectroscopy of the H2-DCN Molecular Complex Keiichi TANAKA, M. Ishiguro, K. Harada1), Y. Sumiyoshi, M. Nakashima, and Y. Endo2) 　 1) Department of Chemistry, Kyushu University , Japan 2) Department of Pure and Applied Science, University of Tokyo, Japan jDCN N C D R H jH2 (Champaign Jun. 25, 2015: RH07)　 1

H2 – HCN/DCN J = l + jH2 + jHCN, K = kH2 + kHCN (S, P ...) Hindered Internal Rotation Almost free rotation jHCN N C H jH2 H z kH2 kHCN R De ≈ 150 cm-1 J = l + jH2 + jHCN, K = kH2 + kHCN (S, P ...) para (IH2= 0, jH2= 0), ortho (IH2= 1, jH2= 1) S0 (K= 0) S0 (K= 0) P0 (K=±1) 40 cm-1 G.S.

MMW Spectrum of H2-DCN Pure rotational transitions Present study 93132 35 MHz oH2 – DCN J = 4 ← 3 F1 = 4 - 4 3 - 3 F1 = 5 - 4 4 - 3 3 - 2 100 150 200 GHz J 3-2 6-5 oH2-DCN (S0) pH2-DCN (S0) Pure rotational transitions 4-3 5-4 Present study J = 1- 0 , 2-1 Transitions FTMW Spectroscopy Internal Rotation of H2 We have assigned pure rotational transitions of para and ortho-H2-HCN previously. 20 GHz 70 GHz

pH2 – DCN F1 = J + IN J = 1 ← 0 F = F1 + ID IN = 1, ID = 1 2 - 1 0 - 1 22235 37 MHz

pH2 – DCN J = 1 ← 0 F1 = 1 – 1 2 1 F 34.6 22235.0 MHz

oH2 - DCN F1 = J + IN (=1) F2 = F1 + IH2 (=1) S0 J = 1 ← 0 F = F2 + ID (=1) 2 - 1 F1 = 1 - 1 0 - 1 23839 41 MHz

oH2 - DCN S0 　J = 1 ← 0 F1 = 1 – 1 F2, F 23839.0 39.5 MHz

oH2 - DCN IN eQq IH2 F2 spin-spin ID eQq F F1 = 0 hf off-diagonal x 10 1 MHz 2 1 1 hf off-diagonal x 10 1 2 1 3 2 J = 1 1 100 kHz 2 1 1 1 2 3 2 1 1 Obs. J = 0 F1 = 1 F2 = 1,0,2 F

B0 D0 eQqN eQqD dH cH 165.8(61) -2.9088(65) 138.0(72) 24.54(65) MHz kHz pH2-DCN oH2-DCN Unit B0 D0 11162.0219(36) 11941.7721(35) 23.3914(20) 10.9870(23) Table I. Molecular Constants of H2-DCN eQqN -3.479(34) ___ ___ cH -1.05(83) kHz

ks 29.31 76.43 mN/m <q >N 24.62(36) 30.29(61) deg p-H2 o-H2 ks 29.31 76.43 mN/m <q >N 24.62(36) 30.29(61) deg R0 4.1593(22) > 4.0034(4) Å H2-DCN 0.16 Å H/D C N p-H2 H/D C N o-H2 ks 28.37 77.85 mN/m <q >N 28.93(27) 33.04(4) deg R0 4.1590(15) > 3.9615(2) Å From the observed rotational constants of H2-HCN and H2-DCN, it have been confirmed that the para hydrogen is attached to the hydrogen side of HCN and the ortho hydrogen is attached to the nitrogen side of HCN. The intermolecular bond length is 4.23 A for para-H2-HCN and 3.96 A for ortho-H2-HCN. H2-HCN 0.20 Å

rs structure of D/H |zD| = 1.807 Ǻ B0 12910.58 11941.77 MHz <R> 3.9615 < 4.0034 Ǻ (kHz) oH2-NCH oH2-NCD unit rs structure of D/H |zD| = 1.807 Ǻ GHCN H D C N |zD| = 1.899 Ǻ |zD| = 1.349 Ǻ G 1.624 0.275 <R> 1.899 Ǻ 1.349

H2-H/DCN in the equilibrium state para-H2 IH2 = 0, jH2 = 0 H + - H C N H De = 145.3 cm-1 a = 0.85 Å3 ortho-H2 IH2 = 1, jH2 = 1 m = 2.99 D H2-HCN complex is a weakly bound molecular complex and the para hydrogen is attached to the hydrogen side of HCN and the ortho hydrogen is attached to the nitrogen side of HCN. The dissociation energies are reported to be 140 and 170 cm-1 for para and ortho species by ab initio calculation. - - + + H C N + H H - Q = 0.66 x 10-26 cgs esu De = 173.2 cm-1

N≡C-H/D Y10 H2 Nuclear Spin-spin Interaction dH 21.89(37) 24.54(65) (kHz) oH2-NCH oH2-NCD <P2(cosq)> 0.380(6) 0.426(11) jHCN N C H R jH2 q Z’ Z free H2 molecule : dH2 = 57.671 (24) kHz Phys. Rev. (1953) H2-HCN Complex : dH = dH2 <P2(cosq)> Pure free rotation H2 jH2 = 1 : <P2(cosq)> S (kH2 = 0 ) : 0.4 P ( “ = ±1 ) : - 0.2 Rotational Wave Function of H2 N≡C-H/D Y10

H2 Nuclear Spin-Rotation Interaction jHCN N C H R jH2 q Z’ Z cH -5.00(64) -1.05(83) cH/2cH2 0.022(3) 0.005(4) (kHz) oH2-HCN oH2-DCN free H2 molecule : cH2 = -113.904 (30) kHz Phys. Rev. (1953) H2-HCN Complex : cH = 2cH2 [Si bi/(EPi-ES0)] Coriolis interaction : S-P mixing ratio ~ cH/2cH2 S0 : P ≤ 2% mixed Y1±1 S0 : nearly of Y10 , Free rotor

Conclusions 1) FTMW and MMW spectra of the para/ortho-H2-HCN/DCN complex have been observed for the ground S0 state. 2) For the ortho-H2 species, hyperfine splittings due to the H nuclear spin (I =1) have been observed. 3) Observed nuclear spin-spin interaction constants dH and the spin-rotation interaction constants cH for the ortho-H2 species show that the H2 part is rotating almost freely in the complex with nearly of K = 0. 4) rs-structure of the ortho-H2 species indicates that H2 is attached to the N side of HCN. Bond lengths for the para-H2 species are longer by 0.15-0.20 Ǻ than that for the ortho-H2 species because H2 is attached to the H side of HCN. 5) Force constant of the bond stretching ks for the ortho-H2 species is about three times larger than that for the the para-H2 species , while the HCN/DCN bending angle <q> for the ortho-H2 species is larger than that for the para-H2 species to accord with PES given by ab initio calculation.

Potential Energy Surface： pH2-HCN, S0 8 6 2 -170 -130 -150 -50 -10 -90 H N C q Å R R R = 4.30 Å 4 V = -171 cm-1 0º 90º 180º H2···HCN q HCN···H2

Potential Energy Surface：oH2-HCN, S0 q Å 8 R -290 -10 -50 -90 -130 -170 -210 -250 6 R 4 R = 3.70 Å V = -309 cm-1 2 0º 90º 180º H2···HCN q HCN···H2