The photodissociation dynamics of methylamines ͑CH 3 NH 2 and CD 3 ND 2 ͒ on the first electronically excited state has been investigated using the velocity map ion imaging technique probing the H or D fragment. Two distinct velocity components are found in the H͑D͒ translational energy distribution, implying the existence of two different reaction pathways for the bond dissociation. The high H͑D͒ velocity component with the small internal energy of the radical fragment is ascribed to the N-H͑D͒ fragmentation via the coupling of S 1 to the upper-lying S 2 repulsive potential energy surface along the N-H͑D͒ bond elongation axis. Dissociation on the ground S 0 state prepared via the nonadiabatic dynamics at the conical intersection should be responsible for the slow H͑D͒ fragment. Several S 1 vibronic states of methylamines including the zero-point level and n 9 states ͑n =1, 2, or 3͒ are exclusively chosen in order to explore the effect of the initial quantum content on the chemical reaction dynamics. The branching ratio of the fast and slow components is found to be sensitive to the initial vibronic state for the N-H bond dissociation of CH 3 NH 2 , whereas it is little affected in the N-D dissociation event of CD 3 ND 2. The fast component is found to be more dominant in the translational distribution of D from CD 3 ND 2 than it is in that of H from CH 3 NH 2. The experimental result is discussed with a plausible mechanism of the conical intersection dynamics.

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There have been many experimental studies of the photolysis of dichlorine monoxide (Cl 2 O), [1][2][3][4][5][6][7][8] Meanwhile, the direct isomerization from ClOCl into ClClO through a transition state (TS S0 ) of S 0 was also suggested in 1998, 5 as another possible explanation for the isomer, but the role of TS S0 in actual dynamical process has not yet been clearly studied theoretically. A later theoretical study in 2001 with reduced two-dimensional space at fixed bond angle showed that the initial dynamics of excited electronic states is the direct dissociation of ClOCl to ClO and Cl, 6 but the possibility of isomerization through angular motion in either the ground or the excited electronic state was not explicitly studied there. Neither the validity of the TS S0 nor the possibility of the direct isomerization has been explicitly examined yet.In addition, Nickolaisen et al. observed unknown vibrational series in their absorption spectrum in the energy region of 20,000 -22,000 cm Since the energies of the light sources (irradiation of light 320 -428 nm corresponds to 3.9 -2.9 eV) used in the detection of ClClO correspond to the first excited singlet state, S 1 ( 1 B 1 ), of ClOCl, 2,7 the detailed dynamical behavior of the S 1 state of ClOCl and ClClO deserves to be studied too. In other word, the possibility of direct isomerization through the potential energy surface (PES) of not only the S 0 state but also the S 1 state deserve to be explored further. However, no reliable theoretical study of the stability, stationary structure, and vibration properties of the S1 electronic states of ClOCl and ClClO has previously been explicitly reported yet. Because the photolysis with higher photon energies opens up more complicated and distinct pathways, 4,7-9 a clearer understanding of the characteristics of S 1 is an indispensable prerequisite of further rigorous dynamical study of the higher excited states of Cl 2 O systems.To provide additional insights on the matters, i.e., the validity and role of the transition state structure involved in the direct isomerization along S 0 PES from ClOCl to ClClO isomer is reexamined in the present work by using highest level of theory applied so far. The stability of the first excited singlet state, S 1 , of both ClOCl and ClClO are also studied here, at first. Details of Computations. The coupled-cluster singles and doubles (CCSD) method10 and its extended CCSD(T) method 11 including non-iterative triples were used for the study of the ground singlet state (S0), whereas the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) method 12 was used for the first excited singlet states (S 1 ). The molecular orbitals (MOs) corresponding to the core atomic orbitals of O (1s) and Cl (1s, 2s, and 2p) atoms were frozen (dropped) in the post Hartree-Fock calculations. The analytic gradient method for the CCSD and EOM-CCSD energies with the dropped MO space not only for the ground state 13 but also for excited states, 14 as implemented in the ACES-2 suit of programs, 15 ...

The spectroscopic constants for the ground (X (1)A(1)) and low-lying triplet and singlet excited states (a (3)A("),A (1)A("),B (1)A(')) of thiocarbonyl chlorofluoride (ClFCS) were obtained using the equation-of-motion coupled-cluster singles and doubles method. The calculated vibrational frequencies of the electronic states were within 4% of the experimental values for 21 of the frequencies, but four calculated frequencies were 20%-40% away from the corresponding experimentally reported values, suggesting the need to reexamine previous experimental spectra. The spectroscopic properties of the radical fragments (FCS, ClCS, and CClF) were also studied, and the correlation diagram between the excited electronic states of ClFCS and possible combinations of dissociation fragments were obtained. The potential energy surfaces (PESs) of the excited electronic states of ClFCS along possible dissociation pathways were also studied. The main qualitative dynamical features of the S(1)(A (1)A("))<--S(2)(B (1)A(')) fluorescence of ClFCS, which may occur in spite of the small barrier (8 kcalmol) on the S(2) PES to the dissociation of C-Cl bond, are discussed.

The low-lying electronic states of carbonyl chlorofluoride (ClFCO) were studied using the coupled-cluster singles and doubles (CCSD) method. Highly reliable values for not only the geometrical parameters, but also the vibrational properties were generated for T 1 and S 1 as well as S 0 . Potential energy surfaces (PESs) of the dissociation of the three bonds were also obtained for each electronic state separately. We found that the T 1 and S 1 states are both vibrationally predissociative along the C-Cl bond dissociation channel, with barrier heights of only 0.13 and 0.23 eV, respectively. The relative energies for the S 1 state of the barriers to C-Cl and C-F bond dissociation are 4.93 and 6.13 eV, respectively, with respect to S 0 . These results suggest that a simple C-Cl bond dissociation pathway can explain the results of a previous photodissociation experiment with 235 nm (5.276 eV) light, in which only 'Cl þ FCO' fragments were observed.

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