Ab initio Studies on Hydrazines: 1H-Pyrrol-1-amine (N-Aminopyrrole)

1988 ◽  
Vol 41 (3) ◽  
pp. 397 ◽  
Author(s):  
NV Riggs ◽  
L Radom
Keyword(s):  
Saddle Point ◽  
Ab Initio ◽  
Pyrrole Ring ◽  
Vibrational Energy ◽  
Zero Point ◽  
Equilibrium Structure ◽  
Basis Sets ◽  
Primary Amines ◽  
Transition Structure ◽  
Zero Point Vibrational Energy

The geometries of four stationary structures of 1H-pyrrol-1-amine have been optimized with the 3-21G and 3-21G(N*) basis sets. The lowest- energy and only equilibrium structure is the 'perpendicular' CS form (4) in which a pyramidal NH2 group is bisected by the plane of the pyrrole ring. The transition structure for inversion at the NH2 group is the perpendicular C2V form (2). After zero-point vibrational -energy corrections, it lies 24.5 kJ mol-1 [3-21G(N*)] above (4). The transition structure for rotation about the N-NH2 bond is the 'parallel' CS form (3) in which a plane of symmetry bisects both the pyrrole ring and the attached pyramidal NH2 group; it lies 26.5 kJ mol-1 above (4). The planar C2V structure (1) is a second-order saddle point lying 69.4 kJ mol-1 above (4). The spacing of NH-stretching frequencies calculated for the equilibrium structure (4) of 1H-pyrrol-1-amine is in the range for normal primary amines, unlike that for 1,1-dimethylhydrazine.

Ab initio Studies on Hydrazines: 4H-1,2,4-Triazol-4-amine

1989 ◽  
Vol 42 (10) ◽  
pp. 1623 ◽  
Author(s):  
NV Riggs
Keyword(s):  
Saddle Point ◽  
Relative Intensity ◽  
Vibrational Energy ◽  
Zero Point ◽  
Equilibrium Structure ◽  
Vibrational Frequencies ◽  
Basis Sets ◽  
Transition Structure ◽  
Intensity Pattern ◽  
Zero Point Vibrational Energy

The geometries of four stationary structures of 4H-1,2,4-triazol-4-amine have been optimized with the 3-21g and 3-21g(N*) basis sets. The lowest-energy and only equilibrium structure predicted by these calculations is the 'perpendicular' CS form (7). All its calculated vibrational frequencies are real and, after zero-point vibrational-energy corrections, it lies 26.9 kJ mol-1 below the 'parallel' C, structure (6), here characterized as the transition structure for internal rotation about the N-NH2 bond (cf. 26.5 kJ mol-1 for the corresponding structures of 1H-pyrrol-1-amine, but only 8.7 kJ mol-1 for the corresponding structures of 2H-1,2,3-triazol-2-amine). The transition structure for inversion at the NH2 centre is, as for 1H-pyrrol-1-amine and 2H-1,2,3-triazol-2-amine, the perpendicular C2v � structure (5), the barrier being 21.4 kJ mol-1 (cf. 24-26 kJ mol-1 for the two reference azolamines ). The planar C2v structure (4) is a second-order saddle point lying 66.6 kJ mol-1 above the equilibrium structure (cf. 69.4 kJ mol-1 for 1H-pyrrol-1-amine, but only 41 .7 kJ mol-1 for 2H-1,2,3-triazol-2-amine). The calculated NH-stretching vibrational frequencies for 4H-1,2,4-triazol-4-amine are c. 20 cm-1 higher than those of 1H-pyrrol-1-amine and their splitting is c. 8 cm-1 greater but they show a very similar relative-intensity pattern, quite unlike that calculated for 2H-1,2,3-triazol-2-amine. ′

An ab initio Study of the Equilibrium Structures of Prop-2-ynamine (Propargylamine) and the Transition Structures Connecting Them

1987 ◽  
Vol 40 (3) ◽  
pp. 435 ◽  
Author(s):  
NV Riggs
Keyword(s):  
Ab Initio ◽  
Internal Rotation ◽  
Vibrational Energy ◽  
Vibrational Analysis ◽  
Zero Point ◽  
Basis Set ◽  
Basis Sets ◽  
Experimental Result ◽  
Transition Structure ◽  
Equilibrium Structures

Optimization with the 3-21G and 3-21G(N*) basis sets finds, in agreement with previous ab initio studies and the experimental result, the anti conformation of prop-2-ynamine to be of lowest energy and, after zero-point vibrational -energy ( Ezpv ) corrections, the gauche form to lie 11 kJ mol-l higher; by vibrational analysis, both are confirmed as equilibrium structures. The synform was not able to be optimized with the 3.21G basis set but, with the 3-21G(N*) basis set, is found to lie 8.6 kJ mol-1 (after Ezpv corrections) above the gauche form, and is shown by vibrational analysis to be a transition structure connecting enantiomeric gauche forms by internal rotation about the N-C bond. The transition structure connecting gauche and anti forms by internal rotation lies 6.3 kJ mol-1 (after Ezpv corrections) above the gauche form, and the transition structure for inversion at the nitrogen atom lies 31.1 kJ mol- l (after Ezpvcorrections) above the anti form.

Ab initio Studies on Hydrazines: 2H-1,2,3-Triazol-2-amine With Special Reference to Its Equilibrium Structure and Vibrational Spectrum

1989 ◽  
Vol 42 (3) ◽  
pp. 433 ◽  
Author(s):  
NV Riggs
Keyword(s):  
Hydrogen Bonding ◽  
Vibrational Energy ◽  
Zero Point ◽  
Equilibrium Structure ◽  
Basis Sets ◽  
Transition Structure ◽  
Hydrogen Atoms ◽  
Ring Nitrogen ◽  
Experimental Values ◽  
Double Hydrogen

The geometries of four stationary structures of 2H-1,2,3-triazol-2-amine have been optimized with the 3-21G and 3-21G(N*) basis sets. The lowest-energy and only equilibrium structure predicted by these calculations is the 'perpendicular' Cs form (3), whereas infrared studies on benzo-annelated analogues had suggested it might be the 'parallel' Cs form (2) stabilized by 'double hydrogen-bonding' of the amino-hydrogen atoms to the flanking ring-nitrogen atoms. The latter form (2) is here characterized as the transition structure for rotation about the N-NH2 bond and, after zero-point vibrational-energy corrections, is calculated to lie 8.7 kJ mol-1 above the equilibrium structure (3) at HF/3-21G(N*) level or only 3.8 kJ mol-1 at MP4/6-31G** level. This very low barrier to internal rotation (cf. 26.5 kJ mol-1 for the analogous 1H-pyrrol-1-amine) may be due to double hydrogen-bonding of the kind suggested by the experimental study mentioned above. The transition structure for inversion at the NH2 centre is, as for 1H-pyrrol-1-amine, the perpendicular C2v structure (5), the barrier being 25.8 kJ mol-1 (cf. 24.5 kJ mol-1 for 1H-pyrrol-1-amine), and the planar C2v structure (4) is a second-order saddle point lying 41.7 kJ mol-1 above the equilibrium structure (3). Calculated NH-stretching frequencies, their separation, and relative intensities as compared with experimental values for benzo-annelated analogues offer broad support for the assignments above based on relative energies.

Ab initio Studies of Hydrazines: Equilibrium Structures of 1,1-Dimethylhydrazine and Transition Structures Connecting Them

1987 ◽  
Vol 40 (11) ◽  
pp. 1783 ◽  
Author(s):  
NV Riggs ◽  
L Radom
Keyword(s):  
Internal Rotation ◽  
Vibrational Energy ◽  
Zero Point ◽  
Basis Set ◽  
Basis Sets ◽  
Primary Amines ◽  
Rotational Angle ◽  
Small Rise ◽  
Equilibrium Structures ◽  
Anti Form

Optimization of the geometries of various stationary structures of 1,1-dimethylhydrazine has been carried out with the 3-21G and 3-21G(N*) basis sets, and the energies of each of the latter optimized structures have been evaluated with the 6.31G* basis set. The gauche form with a (mean) internal rotational angle near 80� (hydrazine, approx. 90�) is the lowest-energy form. After zero-point vibrational -energy corrections, the anti form lies in a shallow well 14kJ mol-1 higher on the potential-energy surface for internal rotation, and the transition structure connecting them lies approx. 1 kJ mol-1 higher still. The anti form is thus a true equilibrium species, unlike the case for hydrazine, but constitutes less than 0.5% of the molecules present at room temperature. It is estimated to have a half-life of less than 10 ps , so its observation by present physical methods may prove to be difficult. The barrier to internal rotation via the syn form (41kJ mol-1) coincides with that for hydrazine. gem-Dimethyl substitution in hydrazine leads to a small rise (1-2 kJ mol-1) in the barrier to inversion at the unsubstituted nitrogen atom, but to an unexpectedly high (by 8-9 kJ mol-1) calculated barrier to inversion at the substituted centre, whether the result be referred to the barrier in hydrazine or to that in dimethylamine. Calculated NH stretching frequencies for the gauche form show a spacing much larger than that for 'simple' primary amines, as is found experimentally.

An ab initio Investigation of the Equilibrium Structures of Hydrazine and of the Transition Structures Connecting Them

1986 ◽  
Vol 39 (12) ◽  
pp. 1917 ◽  
Author(s):  
NV Riggs ◽  
L Radom
Keyword(s):  
Potential Energy ◽  
Ab Initio ◽  
Internal Rotation ◽  
Energy Surface ◽  
Vibrational Energy ◽  
Vibrational Analysis ◽  
Basis Sets ◽  
Transition Structure ◽  
Transition Structures ◽  
Anti Form

An ab initio investigation of the various equilibrium and transition structures of hydrazine has been carried out with full geometry optimization and use of the 3-21G, 3-21G(N*), and 6-31G* basis sets. Best estimates of relative energies (as quoted below) were obtained by evaluation of total electronic energies at the MP3/6-31G**//6-31G* level. By vibrational analysis, it was confirmed that the gauche form is an equilibrium species and that the syn form, which lies 39.8 kJ mol-1 above the gauche form, is a transition structure connecting enantiomeric gauche forms by internal rotation. The anti form, characterized by vibrational analysis as an equilibrium species on the STO-3G, 3-21G, and 6-31G* potential-energy surfaces, lies in a shallow minimum 7.7 kJ mol-1 above the gauche form. A transition structure connecting gauche and anti forms by internal rotation lies, however, only 0.4 kJ mol-1 higher on the electronic-energy surface and, after zero-point vibrational -energy corrections, 0.3 kJ mol-1 below the anti form which is, therefore, the true transition structure. The transition structure for inversion at one nitrogen atom of the gauche form is shown to be a CS structure lying 26.2 kJ mol-1 above the gauche form itself. Various other structures, including those of D2h and D2d symmetry, are discussed briefly and shown by vibrational analysis to be neither equilibrium species nor true transition structures on the 3-21G potential-energy surface. Finally, the complete potential function for internal rotation has been evaluated at levels up to MP3/6-31G**//HF/6- 31G*, and the coefficients of the corresponding four-term Fourier cosine series are presented and briefly discussed.

scholarly journals Transition from Regular to Stochastic Vibrational Motion in H+3 Molecule: An ab initio Classical Trajectory Study

2000 ◽  
Vol 55 (3-4) ◽  
pp. 478-480
Author(s):  
P. Babinec ◽  
E. Jakubíková ◽  
J. Leszczynski
Keyword(s):  
Ab Initio ◽  
Vibrational Energy ◽  
Zero Point ◽  
Classical Trajectory ◽  
Vibrational Motion ◽  
Stochastic Motion ◽  
Vibrational Dynamics ◽  
Zero Point Vibrational Energy

Abstract An ab initio classical trajectory study of intramolecular vibrational dynamics in H+3 molecule revealed a transition from regular quasiperiodic to stochastic motion at an energy slightly higher than the zero point vibrational energy

ON THE NECKING-IN PROCESS IN CLUSTER DECAYS

1990 ◽  
Vol 05 (20) ◽  
pp. 3901-3928 ◽  
Author(s):  
K. DEPTA ◽  
J. A. MARUHN ◽  
HOU-JI WANG ◽  
A. SĂNDULESCU ◽  
W. GREINER ◽  
...  
Keyword(s):  
Potential Energy Surfaces ◽  
Vibrational Energy ◽  
Correction Term ◽  
Zero Point ◽  
Alpha Decay ◽  
Shell Correction ◽  
Macroscopic Models ◽  
Excellent Description ◽  
Energy Surfaces ◽  
Zero Point Vibrational Energy

Two new macroscopic models (liquid drop and Yukawa-plus-exponential) describing the decays with emission of large fragments including alpha decay are developed. The proposed shape parametrization consists of two intersecting spheres smoothly joined by a third "rolling sphere". The first two spheres describe asymptotically the charge and mass asymmetries and the third one the necking-in process. It is shown that the potential energy surfaces in the neck and the relative distance between the centers of the spheres (for a given mass and charge fragmentation) lead to different dynamical paths depending on the mass and charge of the emitted fragment. Along the path a phenomenological shell correction term and a zero point vibrational energy are introduced. It is shown that this model gives an excellent description of the present experimental data.

Zero-point vibrational energy of an adsorbed film

1991 ◽  
Vol 84 (1-2) ◽  
pp. 1-17 ◽  
Author(s):  
James F. Annett ◽  
Milton W. Cole ◽  
Peter B. Shaw ◽  
Richard M. Stratt
Keyword(s):  
Vibrational Energy ◽  
Zero Point ◽  
Adsorbed Film ◽  
Zero Point Vibrational Energy
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