Millimeter-Wave Spectroscopy of the vdW Bands of He- HCN the Dissociation Limit. Millimeter-Wave Spectroscopy of the vdW Bands of He- HCN Above the Dissociation Limit. Millimeter-Wave Spectroscopy of the vdW Bands of He- HCN the Dissociation Limit. Millimeter-Wave Spectroscopy of the vdW Bands of He- HCN Above the Dissociation Limit. Keiichi TANAKA, and K. Harada Keiichi TANAKA, and K. Harada Department of Chemistry, Kyushu University Fukuoka, Japan Keiichi TANAKA, and K. Harada Keiichi TANAKA, and K. Harada Department of Chemistry, Kyushu University Fukuoka, Japan (Columbus. Ohio June 22, 2010) He j N C H R

Internal Rotation of HCN He R N C H D 0 = 9.6 cm  1 He-HCN Complex Dissociation Dissociation  s Intermolecular Stretching j l Complex Rotation of He-HCN G

s He-HCN: Intermolecular Vibration Band j He N C H R  j=2j=2 j=1j=1 s j=0j=0 J 1 0 E cm -1 Dissociation Limit: He + HCN 2 l l * MBER * * * *

250 x 10 j He N C H R  s He-HCN 0 = 98.7 GHz MHz j = 1←0 j = 2←1 j = 2←0 s ←j = 1 s x 10 j = 0 l = 5←4  l

White-type multi-Reflection (10-round trips) Pulsed valve InSb Gunn BWO Grid Polarizer PET Beam Splitter Pump Probe 90 ゜ R=0.15 Millimeter-wave Double Resonance Pump Probe P Q 20 mW 10 mW j = He-HCN T=2K T=2K

MHz Probe ? Pump Off j = E cm -1 1f1f 3f3f j = 1 j = 2 l = 2

Pump Probe MHz F = Pump On Dissociation Limit j = E cm -1 1f1f 3f3f j = 1 j = 2 l = MHz

s j He N C H R  j=2j=2 j=1j=1 j=0j=0 J 1 0 E E cm -1 He + HCN (j=0) He + HCN (j=1) 5 f 3 f 1 f 2 f l l = s f-states f-states e, f-states e, f-states

e level: (-1) | J | = Parity f level: - (-1) |J| = Parity R He j N C H l Conserved: Parity + /  = (-1) |l |+| j|, Energy Total J = l + j Internal rotation Dissociation J R → ∞ l' ' = l' + j' Also Conserved:

|J||J| He + HCN (j’=0) E = b HCN j’(j’+1) + B HeHCN l’(l’+1) + kinetic After Dissociation 2b HCN E = 0 He + HCN (j’=1) He j’ N C H R l’ J l' Dissociation limit for e levels Dissociation limit for f levels l'+1 l' -1 l' G (-1) J-l-j = 1, e -1, f (-1) J-l-j = 1, e -1, f e e e f

s j He N C H R  j=2 j=1 j=0 J 1 0 E E cm -1 He + HCN (j=0) Dissociation Limit for f level: He + HCN (j=1) 5 f 3 f 1 f 2 f Dissociation Limit for e level: 2 e 0 e0 e 4 e 3 e3 e 1 e 4 e4 e 6 e6 e 2 e 3 e 4 e l

He-HCN HCN-He Minimum Energy Path (MEP) He-HCN D e = 29.6 cm -1 MMW+Beam 27 Data+hf PES  ~ 90 kHz

E / cm  1 ° ° ﾟ  He-HCN HCN-He Dissociation Limit Potential Energy Surface along MEP Exp. D 0 = 9.32 cm  1 D e = 29.6 cm  cm  1 j=1 j=2 s 0.4 cm  Toczylowski et al. JCP, (2001)

R ( Å ) 0 ° 90 ° 180 ° 4×10 -9 l = 1 |   j = 2, l = 1, J = 2 f 

Probability Density   in the j = 2, f state He C l = 1, J = 2 0 A   10 0 N C H Stable Bound State

s j He N C H R  j=2 j=1 j=0 J 1 0 E E cm -1 He + HCN (j=0) He + HCN (j=1) 3 f 1 f 2 f 5 f 6 e* 2 f* 4 f* Metastable State Dissociation Limit for e level: l l = Dissociation Limit for f level:

|   e : l = J = 6, j = 0 x 1000 Intermolecular Potential He- HCN Centrifugal barrier cm -1 R (Å)(Å)  90 ° Meta-stable State 0.74 cm -1 V(V( R) + h 2 RR 2 l ( l + 1 )  = 1.8 ns  = 89 MHz  = 1.8 ns  = 89 MHz Tunneling effect 2.5 cm -1

3× °°° Centrifugal barrier l = 6 |   j = 0, l = J = 6 e ( Å )

Metastable States of He-HCN j l J E(cm -1 )  z  ns  e-state ( HCN : j = 0, 0 cm -1 ) f-state ( HCN : j = 1, 2.96 cm -1 )

SUMMARY 1. The internal rotation transitions to the bound f levels above the “Dissociation Limit” have been observed. 2. The e and f levels of He-HCN have different dissociation limits, e levels He + HCN ( j = 0 ) : E = 0 f levels He + HCN ( j = 1 ) : E = 2b HCN due to the conservation of parity and total J. 3. Metastable levels bound by centrifugal barrier have been predicted from PES. SUMMARY 1. The internal rotation transitions to the bound f levels above the “Dissociation Limit” have been observed. 2. The e and f levels of He-HCN have different dissociation limits, e levels He + HCN ( j = 0 ) : E = 0 f levels He + HCN ( j = 1 ) : E = 2b HCN due to the conservation of parity and total J. 3. Metastable levels bound by centrifugal barrier have been predicted from PES.

Hamiltonian b : Rotational constant of HCN  : Reduced mass h2h2 h2h2 Fit to 25 lines,  ~ 90 kHz Short- range Long- range 15 parameter: g i, d i, b i, c 6, c 7, c 8,  -dep V(R,  ) = Born-Mayer Potential PES:HeHCN R 

Predissociation of He-HF Lovejoy and Nesbitt, JCP, 93,5387(1990) 11 00 11 1 j=1 1 j=0 Bound? IR Q(1) Predissociate

10 round trip Roots Pump White-type Multi-reflection Jet Cell He : HCN = 0.3% P= 20 atm Pulsed Jet Nozzle 100Hz 18 inch Diffusion Pump T rot = ~ 2 K Millimeter-wave 79~300 GHz