1. 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

2. 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.

3. MMW Spectrum of H2-DCN Pure rotational transitions Present study
93132 35
MHz
oH2 – DCN
J = 4 ← 3
F1 = 4 - 4
3 - 3
F1 =
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

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

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

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

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

8. 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

9. 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
(36)
(35)
(20)
(23)
Table I. Molecular Constants of H2-DCN
eQqN
-3.479(34)
___
___ cH
-1.05(83)
kHz

10. ks 29.31 76.43 mN/m <q >N 24.62(36) 30.29(61) deg
p-H o-H2
ks mN/m
<q >N (36) (61) deg
R (22) > (4) Å
H2-DCN
0.16 Å
H/D C N
p-H2
H/D C N
o-H2
ks mN/m
<q >N (27) (4) deg
R (15) > (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

11. rs structure of D/H |zD| = 1.807 Ǻ
B MHz
<R> < Ǻ
(kHz) oH2-NCH oH2-NCD unit
rs structure of D/H |zD| = Ǻ
GHCN H D C N
|zD| = Ǻ
|zD| = Ǻ G
1.624
0.275
<R>
1.899 Ǻ
1.349

12. H2-H/DCN in the equilibrium state
para-H2
IH2 = 0,
jH2 = 0 H + - H C N H
De = 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 cgs esu
De = cm-1

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

14. H2 Nuclear Spin-Rotation Interaction
jHCN N C H R
jH2 q Z’ Z
cH (64) (83)
cH/2cH (3) (4)
(kHz) oH2-HCN oH2-DCN
free H2 molecule :
cH2 = (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

15. 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 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.

16. 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

17. 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 = cm-1 2 0º
90º
180º
H2···HCN q
HCN···H2