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 ?