Rydberg state dynamics and fragmentation mechanism of N,N,N',N'-tetramethylmethylenediamine

Fengzi Ling; Ling Cao; Yanmei Wang; Jie Wei; Zhigao Luo; Zhe Hu; Jiyun Qiu; Dejun Liu; Pengfei Wang; Xinli Song; Song Zhang

doi:10.1063/5.0159559

Rydberg state dynamics and fragmentation mechanism of N,N,N',N'-tetramethylmethylenediamine

J Chem Phys. 2023 Jul 28;159(4):044301. doi: 10.1063/5.0159559.

Authors

Fengzi Ling^{1

2}, Ling Cao^{3

4}, Yanmei Wang^{3

4}, Jie Wei^{3

4}, Zhigao Luo¹, Zhe Hu¹, Jiyun Qiu¹, Dejun Liu², Pengfei Wang^{2

5}, Xinli Song^{3

4}, Song Zhang^{3

4}

Affiliations

¹ School of Science, Shenzhen Campus of Sun Yat-sen University, Shenzhen 518107, China.
² Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
³ State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China.
⁴ University of Chinese Academy of Sciences, Beijing 100049, China.
⁵ Key Laboratory of In-Fiber Integrated Optics, Ministry Education of China, Harbin Engineering University, Harbin 150001, China.

PMID: 37486051
DOI: 10.1063/5.0159559

Abstract

The non-adiabatic relaxation processes and the fragmentation dynamics of Rydberg-excited N,N,N',N'-tetramethylmethylenediamine (TMMDA) are investigated using femtosecond time-resolved photoelectron imaging and time-resolved mass spectroscopy. Excitation at 208 nm populates TMMDA in a charge-localized 3p state. Rapid internal conversion (IC) to 3s produces two charge-delocalized conformers with independent time constants and distinct population ratios. As the system explores the 3s potential surface, the structural evolution continues on a 1.55 ps timescale, followed by a slower (12.1 ps) relaxation to the ground state. A thorough comparison of the time-dependent mass and photoelectron spectra suggests that ionization out of the 3p state ends up with the parent ion, the vibrational energy of which is insufficient for the bond cleavage. On the contrary, by virtue of the additional energy acquired by IC from 3p, the internal energy deposited in 3s is available to break the C-N bond, leading to the fragment ion. The fragmentation is found to occur on the ion surface instead of the Rydberg surface.