1. 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

2. 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

3. 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 v7
Energy v9
RN-H

4. 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, (2006).

5. Primary dissociation channels
D0 (cm-1)
CH3NH H + CH3NH ,900
H + CH2NH ,600
CH3 + NH ,300
CH4 + NH ,570
CH2NH + H ,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).

6. 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?

7. 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

8. 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, (2013)
M. Epshtein, Y. Monsa, A. Portnov, and I. Bar, Chem. Phys. Lett. 677, 1 (2017)

9. H photofragment action spectra obtained in CH3NH2 and CD3NH2 predissociation
R. Marom, C. Levi, T. Weiss, S. Rosenwaks, Y. Zeiri, R. Kosloff, and I. Bar, J. Phys. Chem. A 114, 9623 (2010);
R. Marom, T. Weiss, S. Rosenwaks, and I. Bar, J. Chem. Phys. 132, (2010).

10. 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, (2015).

11. Branching ratios and b anisotropy parameters for CH3NH2 and CD3NH2

12. TCRD images, Abel inverted images,TKEDs and action spectrum of CH3ND2
M. Epshtein, Y. Yifrach, A. Portnov, and I. Bar, J. Phys. Chem. Lett. 7, 1717 (2016).

13. TKEDs of D photofragments released in CH3ND2 predissociation

14. 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

15. 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 !