Can Internal Conversion be Controlled by Mode-specific Vibrational Excitation in Polyatomic Molecules? Michael Epshtein, Alexander Portnov and Ilana Bar Department of Physics Ben-Gurion University of the Negev Beer-Sheva 84105 ISRAEL

Introduction Conical intersections - points of degeneracy between electronic states, which act as dynamic funnels for radiationless deactivation of the excited state – playing crucial roles in driving internal conversion in different processes RN-H Energy

Methylamine (CH3NH2) - Why? * appears quite often in organic and biologic building blocks * the smallest member of primary amines possessing, in addition to stretching and bending, inversion motion and internal-rotation * interesting dynamics Energy RN-H

Resonant enhanced two-photon spectroscopy of methylamine isotopologues M. H. Park, K.-W. Choi, Y.S. Choi, and S. K. Kim, J. Chem. Phys. 125, 084311 (2006).

Primary dissociation channels D0 (cm-1) CH3NH2 H + CH3NH 35,900 H + CH2NH2 30,600 CH3 + NH2 29,300 CH4 + NH 25,570 CH2NH + H2 10,600 M. N. R. Ashfold, R. N. Dixon, M. Kono, D. H. Mordaunt, and C. L. Reed, Phil. Trans. R. Soc. Lond. A 355, 1659 (1997) . J. O. Thomas, K. E. Lower, and C. Murray, J. Phys. Chem. A 118, 9844 ( 2014).

Most studies lacked characterization of the starting quantum states on the S1 state and direct examination of state-selective predissociation dynamics Would specific vibrational modes on S1 of CH3NH2 isotopologues affect the branching ratios?

Velocity map imaging (2 + 1) resonance-enhanced multiphoton ionization (REMPI) H+ H+ 2s 2S 2s 2S 1s 2S 1s 2S H+ H+ I * Cylindrically symmetric ion cloud * s(x,y) - a slice through the 3D distribution perpendicular to the symmetry axis * f(x) - the integrated distribution s(x,y) along the y axis - raw ion image * Conversion to a central slice in a 3D velocity map by inverse Abel transform

Ion imaging High velocity photofragments lead to strong Doppler broadening (DB) For an atom traveling in the laboratory frame, the frequency it observes is v - velocity w = wl – kv wl - laser frequency k – wavevector Photofragment detection is accomplished by scanning the probe over the DB profile H atoms can be probed in each laser pulse by two-color reduced Doppler (TCRD) or Doppler-free (DF) (2 + 1) REMPI w = wR + wL – (kR + kL)v selection rules: Dl = 0 and Dm = 0 M. Epshtein, A. Portnov, R. Kupfer, S. Rosenwaks, and I. Bar, J. Chem. Phys. 139, 184201 (2013) M. Epshtein, Y. Monsa, A. Portnov, and I. Bar, Chem. Phys. Lett. 677, 1 (2017)

TCRD velocity map images of H atoms, Abel inverted images and TKEDs CH3NH2 CD3NH2 M. Epshtein, A. Portnov, and I. Bar, Phys. Chem. Chem. Phys. 17, 19607 (2015).

Branching ratios and b anisotropy parameters for CH3NH2 and CD3NH2

D action and R2PI spectra,TCRD images, Abel inverted images and TKEDs for CH3ND2 M. Epshtein, Y. Yifrach, A. Portnov, and I. Bar, J. Phys. Chem. Lett. 7, 1717 (2016).

TKEDs of D photofragments released in CH3ND2 predissociation

TKEDs of H(D) atoms resulting from predissociated methylamine isotopologues CH3NH2 CH3ND2 CD3NH2 CD3ND2 Eint(R) = Ehn – D0(N-H(D)) - Et

Branching ratios, Eint (R) and b parameters vs. excitation energy CH3NH2 CH3ND2 CD3NH2 CD3ND2

Summary • The TCRD and DF techniques allowed to measure entire velocity distributions of the photofragments in each laser pulse • The N-H(D) bond fission leads to fast and slow H(D) photofragments • Anomalous distributions in the branching ratios of the H(D) photofragments, Eint(R) and in b parameters for the isotopologues releasing H atoms  dynamic resonances • These resonances strongly depend on the energy of the initially excited rovibronic states, the evolving vibrational mode on the repulsive S1 part during N−D(H) bond elongation, and the manipulated passage through the CI that leads to radicals with high Eint (R) • Theoretical calculations required

Thank You ! Acknowledgements Michael Epshtein Portnov Alexander Yair Yifrach Yaakov Monsa Afik Shahar Tuval Ben Dosa Yuval Ganot Zion Hazan Gyora Gal $$$ ISF, BSF Thank You !