Transcript ArCS_Endo.ppt

FTMW SPECTROSCOPY AND
DETERMINATION OF THE 3-D POTENTIAL
ENERGY SURFACE FOR Ar-CS
CHISATO NIIDA, MASAKAZU NAKAJIMA, and YASUKI ENDO
Department of Basic Science, The University of Tokyo
YOSHIHIRO SUMIYOSHI
Department of Chemistry and Chemical biology, Gunma University
YASUHIRO OHSHIMA
Department of Photo-Molecular Science, Institute for Molecular Science
HIROSHI KOHGUCHI
Department of Chemistry, Hiroshima University, Higashi-Hiroshima
Atom-Diatom System
Possibility to determine the full 3-dimensional
potential energy surface
Van Der Waals vibrations:
R and q
Diatom vibration: r
Fit all the data including those of isotopomers
and vibrationally excited states
of diatom
Ar
S
θ
R
r
C
Previous Studies for Atom–Diatom
Systems in Our Lab
Rg-SH
・Y. Sumiyoshi et al. J. Chem. Phys., 123, 054324 (2005)
・Y. Sumiyoshi et al. J. Chem. Phys., 123, 054325 (2005)
Rg-OH
・Y. Sumiyoshi et al. J. Chem. Phys., 125, 124307 (2006)
・Y. Sumiyoshi et al. Mol. Phys., 108, 2207 (2010)
Rg-NO
・Y. Sumiyoshi et al. J. Chem. Phys., 127, 184309 (2007)
・Y. Sumiyoshi et al. J. Phys. Chem., 114, 4798 (2010)
SH and OH systems: 3-dimensional potential
NO system: 2-dimensional potential
all are open-shell systems
Current Status of the Studies of Atom–
Diatom Systems
Ar-CO
Analysis for all the reported data including
microwave, mm, sub-mm wave, infrared is in
progress to determine the 3-d potential
by Y. Sumiyoshi (Gumma University)
Ar-CS
Previously, 28 rotatinal lines have been observed,
which were analyzed by a rigid rotor Hamiltonian.
In the present study, we have determined the 3-d
potential
Energy Level Structure of the Atom–
Diatom system
Ar–CS (CS：1S)
heavy diatom
relatively large dipole moment (1.8 D)
limit of the free rotor model?
Free Rotor Model
j : internal rotation angular
momentum of CS
j
L : overall rotation of the complex
J=L+j
K : projection of j and J onto the
complex axis
J
Ar
K
j S
L
K
C
Hamiltonian for the System
Overall rotation with intermolecular potential
Diatom intetnal rotation and vibration
CS potential (fitted to the known data for CS)
Intermolecular Potential
・short range term (repulsive)
・asymptotic term (attractive)
q-dependence
Legendre func.
Initial Potential Parameters
CCSD(T)-F12b/aug-cc-pV5Z
2016 grid points
R : 3.0 – 15 Å,
r : 7 points (re–0.15 Å – re+0.15 Å)
q : 0 –180° at every 30° and 105°)
The calculated energies were fitted to the function
with 56 potential parameters including
the q (= r – re) dependent terms.
S
θ
R
Ar
r
C
Calculation of Energy Levels
Basis Functions
j,M
  R 1q1 j,K
 v (R) vs (q)
j,K
v
vs
Over all Rotation and Diatom Rotation


J,M
j,K
jmax = 20
2J 1 J 
2 j 1 j 

DM ,K , ,0 
DK q ,,0
4
4
Intermolecular stretch and monomer vibration

v (R)
v (q)
s

vmax = 18
vsmax = 6 (anharmonic vibration)
numerical diagonalization of the matrices
up to N=10,000
Energy Level Diagram of Ar–CS
splitting of the energy levels
by the anisotropic potential
red: observed levels
Observaton of the Spectra
Ar + CS2 (0.1%)
FTMW spectroscopy
(4-40 GHz)
FTMW mm-wave DR
(60–70 GHz)
electric discharge
C32S
vs=0
vs=1
vs=2
C34S
vs=0
36 lines
24 lines
22 lines
Ar-CS
J,K = 2,2–3,1
16 lines
J,K = 1,1–1,0
Results
All the observed data were fitted wih s = 46 kHz
Adjusted 13 parameters among 56 pot. params.
The fitted potential energy surface at q = 0
The most stable
structure
(T-Shaped)
Ar
R = 3.966 Å
θ = 109.5°
C
r = 1.5348 Å
q
R
S
Energy along the Minimum Energy Path
Ar–SC
Ar–CS
fitted
Large discrepancey
at the linear config.
ab initio
present data: limited to the region around the energy
minimum (amplitude of the vibration is smaller)
Intermolecular Distance along the
Minimum Energy Path
R/Å
fitted
ab initio
0.022 Å
0.030 Å
0.0047 Å
angle / °
fairly good agreement in a limited region
q-Dependence of the Potential
R/Å
q = -0.1 Å
q= 0
Å
q = 0.1 Å
energy / cm–1
Potential is deeper when r (q) is larger
Conclusions
More than 100 rotational transitions were observed
for the Ar–CS complex, including those of excited
vibrational states (vs = 1, 2) and the 34S isotopomer.
All the data were fitted to determine the 3-d potential
energy surface with the standard deviation 46 kHz.
Fairly accurate potential energy surface has been
determined around the minimum.
However, a large discrepancy has been observed
around the linear configuration.
Molecular constants
Ar-C32S (MHz)
Ar-C34S (MHz)
A
27908.04
A
27466.58
B
1519.16
B
1487.39
C
1395.03
C
1364.56
ΔIeff.
―
ΔIeff.
11.49 amu･Å2
H. Kohguchi, master’s thesis (1993)
near prolate molecule