bonding & dynamics of cn-rg and c 2 -rg complexes jiande han, udo schnupf, dana philen millard...
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Bonding & dynamics of CN-Rg and C2-Rg complexes
Jiande Han, Udo Schnupf, Dana Philen
Millard Alexander (U of Md)
Unusual properties of C2-Rg complexes
Theory predicts linear equilibrium structure.The potential energy surfaces do not showsecondary minima for the T-shaped geometry(complete disagreement with the pair potentialmodel)
Data for matrix isolated C2-Xe indicateschemical bond formation
Probe laser
Fluorescence dispersed by0.25 m monochromator
Pulsed valve
C2Cl4+Rg
193 nm Photolysis
Experimentaltechnique
43172.5 43190.0 43207.5 43225.0
Fluo
resc
ence
Int
ensi
ty
Energy /cm-1
ba
** cd
R(0) 0-0
R(0) 1-1
R(0) 2-2
Laser excitation spectrum of the D1+-X1+
transitions of C2 and C2-Ne
43218.0 43219.0 43220.0 43221.0 43222.0 43223.0
Energy /cm -1
exp.
calc.
1357P(J)
R(J)* C2 P(1)
Rotationally resolved spectrum of C2-Ne band a
B’=0.091 cm-1
B”=0.100 cm-1
Rigid rotorparallel bandsimulation
43225.0 43226.0 43227.0 43228.0 43229.0 43230.0 43231.0
Energy /cm-1
exp.
calc.
1 3 5R(J)P(J)
Q(J)
7
Rotationally resolved spectrum of C2-Ne band b
B’=0.108 cm-1
B”=0.100 cm-1
Rigid rotorperpendicular band simulation
+
+
±
±
±
-01
2
+
+
-01
2
R(0
)
R(1
)
P(1
)
R(1
)
Q(2
)
Q(1
)
P(2
)
12
3
J
a b
C2-Ne
X
1g j=0
1uD j=1
K=1
K=0
K=0R
(2)
Main results for C2-Ne
Coriolis interaction between K=0 and K=1 levelsinfluences rotational constants. Deperturbationyields B’=0.100 cm-1 for both manifolds.
E(K=1)>E(K=0) shows that C2(D)-Ne has a linearequilibrium geometry. The barrier to internalrotation is 15 cm-1.
B”(exp)=0.100 cm-1, B”(theory)=0.0996 cm-1
Electronically excited state is slightly moredeeply bound, D0’=D0”+9.7 cm-1
(D0”(theory)=31.6 cm-1)
LIF was not observed from C2-Ar, probablydue to electronic predissociation
CN-Rg examined as the predissociationscan be followed easily using OODRtechniques
Bonding for CN-Xe appears to be unusuallystrong
0
5000
10000
15000
20000
25000
30000
35000
0.9 1.1 1.3 1.5 1.7
r /Å
A2
X2+
B2+
0
1
2
3
4
5
6
7
8
9
10
11
0
1
2
3
4
5
6
7
8
9
100
1
2
CN
Complexes detected via the B-X andA-X transitions of CN
E(cm-1)
JCP 100, 5387 (1994)
387.6 387.8 388 388.2 388.4
R(0)
R(1)
P(1)
b1
b2
b3
b4
a3
a2
a1
Wavelength /nm
Laser excitation spectrum of the CN-ArB-X transition
A-X
flu
ore
scen
ce i
nte
nsi
ty
-3.0 -2.0 -1.0 0.0 1.0 2.0 3.0
cm-1
Band a3
B’=0.080 cm-1
B”=0.069 cm-1
T=3 K
E=-6.4 cm-1
|P|=1
Rotationally resolved band of CN-Ar
Rigid rotorsimulation
-2.0 -1.0 0.0 1.0 2.0 3.0
Relative energy /cm-1
B’=0.075
B”=0.067
T=3 K
E=-10.6cm-1
|P|=0
Band a2
Rigid rotor simulation
Rotationally resolved band of CN-Ar
14350 14400 14450 14500 14550
Energy /cm-1
CN-Ar Fluorescence depletion
CN LI F
detect
B2+
A2
X2
pumpprobe23/2
21/2
Fluorescence depletion spectrum for the A-X 3-0 band of CN-Ar
14398 14444 14490 14536 14582
Energy /cm-1
CN Q1(3/2)
CN(j=3/2)+Ar
112 cm-1
CN(X)+Ar
CN(A,j=3/2)+Ar
CN(B)
Q1(3/2)
Action spectrum for CN-Ar A23/2-Xprovides a direct measurement of D0”
h1
h2
B-X
flu
ore
scen
ce
Energy h1 /cm-1
CN(X)-Ar
Experiment yields D0”=112±1 cm-1, B0”=0.068 cm-1
Best available ab initio potential energy surfacepredicted D0”=62.5 cm-1, B0”=0.062 cm-1
New surfaces were generated for the X and B states
Method: state averaged RHF-CASSCF-RSPT2 Counterposie corrected
Basis set: aug-pvtz with mid-bond functions
Code: MOLPRO
U
R /a
u
/degrees
Potential energy surface for CN(X)-Ar
C
NAr
r
R
Jacobi coordinates
The global minimum is atE=-138.9 cm-1, Re=7.23 au, e=46.8º
U
/degrees
R /a
u
Potential energy surface for CN(B)-Ar
The global minimum is atE=-256.4 cm-1, Re=6.75 au, e=180º
C N Arr
R
Zero-point wavefunctions for CN-Ar
X B
Predicted red shift of origin = 70 cm-1 (not observed)
Good agreement with X state D0 and B0
D0=115 cm-1
B0=0.070
D0=185 cm-1
B0=0.080
(Millard Alexander / HIBRIDON)
Adiabatic bender curves for CN(B)-Ar
High density of vibronically excited states,intensity calculations needed for assignment
MHA / HIBRIDON
Excited state wavefunctions for CN(B)-Ar
MHA / HIBRIDON
400 450 500 550 600 650 700 750 800
9-4
8-3
9-5
9-3
8-49-2
CN A-X
Wavelength /nm
18970 18984 18998 19012 19026
Energy /cm-1
Dispersed fluorescence CN B-A 9-9 LIF
t=200 ns
Detection of the CN(A) fragment followingCN(B,v=0)-Ar CN(A) + Ar predissociation
-5 10 -7 0 5 10-7 1 10-6 1.5 10 -6 2 10-6 2.5 10 -6 3 10-6
Time /s
IF maximum at 800 ns
A-X
Flu
o res
cenc
e I n
tens
i ty
Fluorescence from CN(A) followingpredissociation of CN(B)-Ar
Radiativelifetime of
CN(B) is 60 ns
?!
385.5 386.0 386.5 387.0 387.5 388.0 388.5
1
2
34
CNCN-Kr
Wavelength /nm
Figure 3. Action spectrum of the CN-Kr B-X bands
A-X
Flu
ores
cenc
e In
tens
ity
Laser excitation spectrum of the B-X systemof CN-Kr
No red shifted bands
Emission from CN(A)v=9 and 8
30 cm-1 stretch progression
JCP 100, 5387 (1994)
385.5 386 386.5 387 387.5 388 388.5
1
2
3
4
CNCN-Xe
Wavelength /nm
A-X
Flu
o res
cenc
e In
tens
i ty
Laser excitation spectrum of the B-X systemof CN-Xe
No red shifted bands
Emission from CN(A)v=9 and 8
39 cm-1 stretch progression
Conclusions for CN-Kr, Xe
It is expected that linear CN(B)-Kr, Xe potentialsare much more deeply bound than typical vander Waals wells (stabilized by charge transfercontributions).
Spectra show blue shifted bands with typical vdWvibrational frequencies - implies that the Franck-Condon factors do not provide access to the mostdeeply bound levels.
Contrast between gas-phase and matrix data forCN-Xe shows that many-body forces are importantin the matrix environment.
A2+-X2 spectrum of matrix isolated OH-Xe
Emission spectrum of OHXe red shifted by >8000 cm-1
32433.7 32467.5 32501.2 32535.0
Energy /cm-1
*
**
P1(3/2)
Q1(3/2)
R1(3/2)
OH-Xe
A2+-X2 spectrum of gas phase OH-Xe
Blue-degradedcontours (B’>B”)
26 cm-1 stretchprogression
Low resolutionemission spectrumis the same as thatfor free OH
-5 10 -7 0 5 10-7 1 10-6 1.5 10 -6 2 10-6 2.5 10 -6
Time /s
Fluorescence decay lifetimes for OH(A)and OH(A)-Xe
OH
OHXe
OH(A)Xe OH(X) + Xe ?