Bonding & dynamics of CN-Rg and C 2 -Rg complexes Jiande Han, Udo Schnupf, Dana Philen Millard Alexander (U of Md)

Unusual properties of C 2 -Rg complexes Theory predicts linear equilibrium structure. The potential energy surfaces do not show secondary minima for the T-shaped geometry (complete disagreement with the pair potential model) Data for matrix isolated C 2 -Xe indicates chemical bond formation

Probe laser Fluorescence dispersed by 0.25 m monochromator Pulsed valve C 2 Cl 4 +Rg 193 nm Photolysis Experimental technique

Laser excitation spectrum of the D 1  + -X 1  + transitions of C 2 and C 2 -Ne

C 2 P(1) Rotationally resolved spectrum of C 2 -Ne band a B’=0.091 cm -1 B”=0.100 cm -1 Rigid rotor parallel band simulation

Rotationally resolved spectrum of C 2 -Ne band b B’=0.108 cm -1 B”=0.100 cm -1 Rigid rotor perpendicular band simulation

Main results for C 2 -Ne Coriolis interaction between K=0 and K=1 levels influences rotational constants. Deperturbation yields B’=0.100 cm -1 for both manifolds. E(K=1)>E(K=0) shows that C 2 (D)-Ne has a linear equilibrium geometry. The barrier to internal rotation is 15 cm -1. B”(exp)=0.100 cm -1,B”(theory)= cm -1 Electronically excited state is slightly more deeply bound, D 0 ’=D 0 ”+9.7 cm -1 (D 0 ”(theory)=31.6 cm -1 )

LIF was not observed from C 2 -Ar, probably due to electronic predissociation CN-Rg examined as the predissociations can be followed easily using OODR techniques Bonding for CN-Xe appears to be unusually strong

Complexes detected via the B-X and A-X transitions of CN E(cm -1 )

JCP 100, 5387 (1994)

Laser excitation spectrum of the CN-Ar B-X transition A-X fluorescence intensity

Band a 3 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 rotor simulation

B’=0.075 B”=0.067 T=3 K  E=-10.6cm -1 |  P|=0 Band a 2 Rigid rotor simulation Rotationally resolved band of CN-Ar

detect B2+B2+ A2A2 X2X2 pumpprobe 2  3/2 2  1/2 Fluorescence depletion spectrum for the A-X 3-0 band of CN-Ar

CN Q 1 (3/2) CN(j=3/2)+Ar 112 cm -1 CN(X)+Ar CN(A,j=3/2)+Ar CN(B) Q 1 (3/2) Action spectrum for CN-Ar A 2  3/2 -X provides a direct measurement of D 0 ” h 1 h 2 B-X fluorescence Energy h 1 /cm -1

CN(X)-Ar Experiment yields D 0 ”=112±1 cm -1, B 0 ”=0.068 cm -1 Best available ab initio potential energy surface predicted D 0 ”=62.5 cm -1, B 0 ”=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

R /au  /degrees Potential energy surface for CN(X)-Ar C N Ar r R  Jacobi coordinates The global minimum is at E= cm -1, R e =7.23 au,  e =46.8º

 /degrees R /au Potential energy surface for CN(B)-Ar The global minimum is at E= cm -1, R e =6.75 au,  e =180º C N Ar r R

Zero-point wavefunctions for CN-Ar XB Predicted red shift of origin = 70 cm -1 (not observed) Good agreement with X state D 0 and B 0 D 0 =115 cm -1 B 0 =0.070 D 0 =185 cm -1 B 0 =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

Dispersed fluorescenceCN B-A 9-9 LIF  t=200 ns Detection of the CN(A) fragment following CN(B,v=0)-Ar  CN(A) + Ar predissociation

I F maximum at 800 ns A-X Fluorescence Intensity Fluorescence from CN(A) following predissociation of CN(B)-Ar Radiative lifetime of CN(B) is 60 ns ?!

A-X Fluorescence Intensity Laser excitation spectrum of the B-X system of CN-Kr No red shifted bands Emission from CN(A) v=9 and 8  30 cm -1 stretch progression

JCP 100, 5387 (1994)

A-X Fluorescence Intensity Laser excitation spectrum of the B-X system of 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 potentials are much more deeply bound than typical van der Waals wells (stabilized by charge transfer contributions). Spectra show blue shifted bands with typical vdW vibrational frequencies - implies that the Franck- Condon factors do not provide access to the most deeply bound levels. Contrast between gas-phase and matrix data for CN-Xe shows that many-body forces are important in the matrix environment.

A 2  + -X 2  spectrum of matrix isolated OH-Xe Emission spectrum of OHXe red shifted by >8000 cm -1

A 2  + -X 2  spectrum of gas phase OH-Xe Blue-degraded contours (B’>B”) 26 cm -1 stretch progression Low resolution emission spectrum is the same as that for free OH

Fluorescence decay lifetimes for OH(A) and OH(A)-Xe OH OHXe OH(A)Xe  OH(X) + Xe ?