Keietsu Tamagake

Internal rotation in ethylamine: A treatment as a two-top problem

The infrared absorption spectra of eight isotopic ethylamine molecules, i.e., CH3CH2NH2, CD3CH2NH2, CH3CD2NH2, CD3CD2NH2, CH3CH2ND2, CD3CJ2ND2, CH3CD2ND2, and CD3CD2ND2, have been examined in the vapor phase in the 300–100 cm−1 region. Several Q‐branch peaks were observed for each isotopic species and assigned to the torsional oscillations of the methyl and amino groups of the trans and gauche isomers. The energy levels were calculated on the basis of a coupled two‐top system. The analysis yielded a probable potential function for the internal rotation about the C–N bond of the form V (α) = (316.5/2)(1−cosα)−(11.3/2)(1−cos2α)+(713.7/2)(1−cos3α) −(25.0/2)(1−cos4α)+(25.0/2)(1−cos5α)−(3.7/2)(1−cos6α). The difference between the potential energy minima of the trans and gauche conformations is about 230 cm−1, the trans being the more stable form. It has been concluded that the axis of internal rotation of the amino group does not coincide with the N–C bond but is along a line about 4.5° from the N–C bond and i...

Amino Wagging and Inversion in Methylamines

Fine structures have been observed of the amino‐wagging bands at 780 cm—1 of CH314NH2, at 776 cm—1 of CH315NH2, at 625 cm—1 of CH314ND2, and at 689 cm—1 of CH314NHD. For each vibration—rotation line an appreciable inversion splitting is observed. There is a marked coupling found between the inversion and the internal rotation; and the amount of the inversion splitting of each absorption line depends greatly upon the internal rotation quantum number σ (=0, +1, or —1) and the over‐all rotation quantum number K of the state in question. A hypothetical inversion splitting when the coupling were absent is estimated to be 31.6 cm—1 for the first excited state of the amino‐wagging vibration of CH314NH2.

Amino wagging and inversion in methylamines: Part II. CH3ND2 and CD3NH2

Abstract Fine structure of the amino-wagging band at 625 cm −1 of CH 3 ND 2 has been reexamined, and that at 740 cm −1 of CD 3 NH 2 has been newly observed. Analysis of the spectra was made on the basis of the previously described theory for the coupling of the internal rotation and inversion of the methylamine molecule. A hypothetical inversion splitting when the coupling were absent is estimated to be 13 cm −1 for the first excited state of CH 3 ND 2 , and 18 cm −1 for the first excited state of CD 3 NH 2 . The barrier height is estimated to be 1688 cm −1 in the wagging-inversion double-minimum potential in CH 3 NH 2 .

Amino wagging and inversion in hydrazines: Antisymmetric wagging band of NH2NH2

Abstract The fine structure of the 937 cm−1 band of undeuterated hydrazine in the gaseous state has been observed with a resolving power of 0.3 cm−1. It has been found that every vibration-rotation line splits into four components, and that the amounts of the splittings depend only slightly upon the rotational quantum number K. This fine structure was explained by considering (1) that the band is caused by a vibration in which the wagging motions of the two amino groups take place antisymmetrically with respect to the C2 axis, (2) that along this coordinate an appreciable inversion takes place, (3) that such an inversion results in four equivalent equilibrium conformations of the molecule one after another, and (4) that the barrier height between every two adjacent equilibrium conformations is 2620 cm−1.

Internal Rotation Spectra of Methylamines. I. CH3NH2 and CH3ND2

Infrared absorption spectra of methylamine (CH3NH2) and methylamine‐d2 (CH2ND2) have been observed in the gaseous states in the region of 500–80 cm–1 (20–125 μ). A complicated, irregular structure is observed all over the spectral region, which is attributable to the internal rotation coupled with an over‐all rotation of the molecule. The internal and over‐all rotation energy levels were calculated on the basis of the previously determined molecular parameters and a potential function for the internal rotation (x) with the form of V(x) = 12H3(1‐cos3x) + 12H6(1‐cos6x). The frequencies and intensities for radiative transitions between these energy levels were then calculated. On comparing the results of the calculation with the observed spectra, it has been found that we need to revise the values of the potential constants and one of the molecular constants C2 (the moment of inertia of the methyl group around its own symmetry axis) from what were determined previously with microwave data. The new set of val...

Internal‐Rotational Spectra of Methylamines. II. The Fundamental Torsional Band of CH2DNH2

The infrared absorption spectrum of CH2DNH2 gas has been examined in the 310–80‐cm−1 region. A relatively simple fine structure observed in the 300–260‐cm−1 region was assigned to that of the fundamental band designated as n = 1 ← 0, where n is the vibrational quantum number of the torsional oscillation of the CH2D group with respect to the amino group. It is shown that, in the ground state (n = 0) and in the first excited state (n = 1), there are well‐defined trans and gauche rotational isomers and that each of the gauche levels at n = 1 splits into two with a separation of about 2.8 cm−1 due to the resonance between the two equivalent gauche positions. It is shown, on the other hand, that, in the higher excited states with n ≥ 2, the internal rotation couples strongly with over‐all rotation, so that the fine structures of the hot bands (n = 2 ← 1, 37 ← 2, etc.) are apparently complicated. Such an energy‐level structure of the internal rotation in CH2DNH2 is mainly attributable to the situation that the ...

Inversion and internal rotation in methyl-d-amine: Microwave spectrum

Abstract The microwave spectrum of CH2DNH2 has been observed in the 8–74 GHz region. The spectrum shows that this molecule takes essentially two distinguishable conformers, trans and gauche forms, although a small amount of coupling between them can be detected. For each line of the trans form a small inversion splitting has been found. It is 93.97 MHz at K = 0 and a periodic function of K. The mean frequencies of the inversion pairs of lines are well explained as the frequencies of a rigid rotor. The gauche spectrum is extremely complicated; each rotational line splits into four because of inversion and gauche-gauche tunneling interactions. The analysis was carried out based on the theory developed in the preceding paper. Tunneling energy parameters of internal-rotation, ϵgg and ϵtg, and inversion, δgg and δtg, were determined as ϵgg = 3476.6 MHz, ϵtg = 3233.1 MHz, δgg = 2790.6 MHz and δtg = 3052.7 MHz. Energy difference between trans and gauche conformers ΔEtg was estimated to be 7.060 cm−1 from these values of parameters and also on the basis of the observed anomaly in the Q branch series of trans form which is due to an accidental degeneracy between the K = 1 level of trans and K = 2 level of gauche. The effects on the internal-rotation of other internal motions have also been discussed.

Torsional bands of hydroxylamine

Abstract Infrared absorption spectrum of NH 2 OH has been observed in its gaseous state, and the fine structures of the bands at 386 and 751 cm −1 assignable, respectively, to the fundamental and overtone of the torsional vibration of this molecule have been examined. Band center frequencies for the n = 1 ← 0, 2 ← 1, 3 ← 2, 2 ← 0, and 3 ← 1 transitions (where n is the vibrational quantum number of the torsional oscillation) have been determined to be 386.2, 365.1, 346.3, 751.2, and 711.3 cm −1 , respectively. On the basis of these data, a discussion is given on the internal-rotation potential function.

Inversion and internal rotation in methyl-d-amine: Theory

Abstract A theory has been developed for an analysis of the microwave spectrum of the CH2DNH2-type molecule which has an asymmetric internal rotor. First, the Hamiltonian matrix was expressed on the basis of localized wavefunctions, each of which corresponds to a conformer vibrating in the vicinity of a potential minimum. Next, by a symmetrization, the Hamiltonian matrix was factored into four submatrices. By solving these matrices, a general view of the energy-level structure has been given, which should be useful for an interpretation of the observed rotational spectrum. It has been shown that the inversion splitting in each level of the trans form molecule should be sensitive to the amount of trans-gauche coupling through tunneling and therefore the relative height of a trans level with respect to a gauche level can be determined from an observation of the inversion splitting in the trans levels.

Inversion coordinate and barrier height for the asymmetric amino group NHD in methylamine-d

Abstract A simple theory of asymmetric inverter has been developed in a proper approximation for an interpretation of the inversion splittings observed in the microwave and infrared spectra of CH 3 NHD. It has been shown that there is an appreciable coupling between the inversion and the internal rotation in the CH 3 NHD molecule, and the mode of coupling is somewhat different from that in the CH 3 NH 2 or CH 3 ND 2 with a symmetric inverter. On the basis of this difference, information on the inversion path in the CH 3 NHD molecule has been obtained. A hypothetical inversion splitting when the coupling is absent is estimated to be 0.34 cm −1 for the vibrational ground state and 10.0 cm −1 for the first excited state of the amino-wagging vibration (at 688.2 cm −1 ). From these values, the height of the potential barrier for the inversion has been estimated to be 1765 cm −1 .