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Vibrational structures of methylamine isotopomers in the predissociative states: , , , and
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Image of FIG. 1.
FIG. 1.

R2PI excitation spectra of six methylamine isotopomers (, , , , , and ) in the range. Arrows indicate the spectral origin positions.

Image of FIG. 2.
FIG. 2.

(a) The origin band of in the transition shown with (b) the simulation based on the internal/overall rotational Hamiltonian (see the text for details).

Image of FIG. 3.
FIG. 3.

(a) The R2PI spectrum of for the ( rock) and ( wag) vibronic bands with (b) the simulation based on parameters listed in Table I. The normal mode description for and is given. The relatively poor simulation to the experiment in the high internal energy range is possibly due to vibronic couplings to optically dark states (see the text).

Image of FIG. 4.
FIG. 4.

The calculated torsional potential energy curves in the zero-point energy level (∎), with the wagging mode excitation (●), or with rocking mode excitation (엯) plotted vs the torsional angle around the C–N axis. The calculation was carried out by using the CIS method with the basis set.


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Table I.

Parameters used in the simulation for excitation spectra. Parameters in parentheses are less reliable. is used for all simulations.

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Table II.

Experimental and theoretical band origins of various methylamine isotopomers .

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Table III.

Measured electronic origins and term values for the vibrational levels of six methylamine isotopomers in the state. The numbers in parentheses are the differences between the measured values and fitted ones (see the text for details).

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Table IV.

Ab initio vibrational frequencies of methylamines in the states. The torsional mode was not included. The symmetry species is classified according to the MS group of Cs where the molecular plane containing a C–H bond bisects the HNH angle. The symmetry consideration for the torsional mode in the CNPI group of has been given in Ref. 17.

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Table V.

Harmonic frequencies and anharmonicity constants obtained from fitting the vibrational term values in Table III to Eq. (4).

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Table VI.

The torsional barrier height calculated for the excited, ground, and cationic states of .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Vibrational structures of methylamine isotopomers in the predissociative à states: CH3NHD, CD3NH2, CD3NHD, and CD3ND2