Electronic spectroscopy of DCF Haiyan Fan, Mihaela Deselnicu, Chong Tao, Calvin Mukarakate, Ionela Ionescu and Scott Reid* Department of Chemistry, Marquette University, P. O. Box 1881 Milwaukee, WI 53201-1881 60th International Symposium on Molecular Spectroscopy

HCF: A case study for the RT effect HCF represents a case of the Renner-Teller (RT) effect where both states have large barriers to linearity (Other Examples: CCl2, SiH2) Why is this interesting? The RT interaction is largest near the barrier region, where the wavefunctions overlap most strongly. Thus, one can view the onset of the RT interaction. In HCF, the two singlet states correlate with 1D in the linear configuration. Ã1A ã3A Energy X1A q

HCF: A case study for the RT effect In HCF, the onset of the barrier to linearity is observed in: an increase of A rotational constant with bending excitation fluorescence lifetime lengthening for K ≥ 1, due to onset of strong RT effects as the barrier is approached

Objectives of the present work Building upon our previous studies of HCF, we wish to probe the spectroscopy and dynamics of the Renner-Teller effect in DCF using: Fluorescence Excitation Spectroscopy Fluorescence lifetime measurements Polarization Quantum Beat spectroscopy Determine excited state barriers to linearity and dissociation Compare our results with high level electronic structure calculations

Experimental Details DCF is generated from CD3F using a pulsed discharge source and probed using laser induced fluorescence Lifetime measurements use on-axis geometry to minimize effects from fly-out HV G laser

Fluorescence excitation spectrum of DCF: (0,0,0) 3 2 1 2 1 K Trot ~ 15 K

Fluorescence excitation spectra of (0,u2,0) states 4 3 2 1

A  Ia-1 Variation in A rotational constant with quanta of bend for à state a A  Ia-1 small A large A The A constant increases dramatically with bending excitation, signifying the approach to linearity

Variation in vibrational intervals for pure bending states (0,u2,0), K = 0 “Dixon dip” occurs at barrier to linearity

Dixon plot of vibrational intervals for pure bending states (0,u2,0), K = 0 Quadratic fit yields a barrier height of 6660  430 cm-1 Recent theoretical estimate: 6770 cm-1 Schmidt, et al. Chem. Phys. Lett. 292, 80 (1998)

à state vibrational parameters for HCF and DCF

Probing the barrier to dissociation The highest level observed to date using LIF is the Ka = 0 level of (1,8,0), corresponding to a vibrational energy of 8048 cm-1 above the vibrationless level of the à state In HCF, the highest level we observed using LIF is the Ka = 1 level of (1,6,0), corresponding to a vibrational energy of 8555 cm-1 above the vibrationless level of the à state We thus set a lower limit on the dissociation energy in the à state of 8555 cm-1, which is consistent with a recent theoretical estimate of 8955 cm-1 Schmidt, et al. Chem. Phys. Lett. 292, 80 (1998)

Summary and Conclusions The Renner-Teller effect in DCF has been investigated through fluorescence excitation spectroscopy The onset of the barrier to linearity is observed in: a minimum in the bending vibrational intervals an increase of A rotational constant with bending excitation The derived barrier height is in excellent agreement with theory

Acknowledgements People: Haiyan Fan (Ph.D. 2004) Ionela Ionescu (M.S. 2004) Eduard Ionescu (M.S. 2004) Chris Annesley (undergrad) Joseph Cummins (undergrad) Matthew Bowers (undergrad) Dr. Ju Xin (Bloomsburg U.) Funding: NSF ACS/PRF