Assignment, fit, and theoretical discussion of the ν10 band of acetaldehyde near 509cm−1

Analysis of the rotational spectrum of pyruvonitrile up to 324 GHz

“…On the other hand q and b for the in-plane bending satellite are appreciably different than for the ground state. Similar behavior has been found for the m 10 in-plane scissor mode in acetaldehyde [43], for which q = 0.030903(9) is appreciably smaller than q = 0.3334654 (7) for the stack of torsional states. It is, indeed, reasonable to expect that a normal mode active in the plane containing the rotation axis of the methyl group will have an appreciable effect on the coupling of the torsional motion with rotation, and such information can perhaps be exploited further.…”

Asymmetric-top molecules containing one methyl-like internal rotor: Methods and codes for fitting and predicting spectra

“…As shown in Table 3, most of the studies involve microwave and far-infrared torsional transitions for molecules such as methanol, acetaldehyde, acetic acid, acetamide, methyl carbamate, methyl formate and some peptide mimetics [6,7,[50][51][52][53][54][55][56][57][58][59][60][61][62][63], but some involve in addition vibration-rotation bands in the infrared, e.g., papers on acetaldehyde and methanol [64][65][66][67][68][69][70][71][72][73][74]. Some molecules were relatively heavy, with a small A rotational constant (0.6 cm À1 for methyl formate HCOOCH 3 for example), leading to the observation of J values up to above 70.…”

“…It thus provides an excellent example of an isolated small-amplitude fundamental (bright state) embedded in a bath of dark states. Several thousand transitions in the m 10 band were assigned (with J 6 28, K 6 12), and a simultaneous fit of over 2400 of these transitions (J 6 15, K 6 9) with over 8100 transitions to the torsional bath state has been carried out [71]. Three vibration-torsion interactions, which give rise to rather global level shifts of the order of 1 cm À1 in the m 10 levels, have been identified and quantitatively fit.…”

A Hybrid Program for Fitting Rotationally Resolved Spectra of Floppy Molecules with One Large-Amplitude Rotatory Motion and One Large-Amplitude Oscillatory Motion

“…The full torsion-wagging-rotation Hamiltonian matrices used in the second diagonalization step of our program for this problem of two LAMs and overall rotation has a structure that is superficially similar to the partitioned Hamiltonian matrix used earlier to discuss the 509 cm −1 fundamental vibrational state of acetaldehyde embedded in a bath of torsional states built upon the ground vibrational state. 15 We first separate the set of non-degenerate states (of species twr A 1 ⊕ twr A 2 ⊕ twr B 1 ⊕ twr B 2 ) from the set of doubly degenerate states (of species twr E 1 ⊕ twr E 2 ) using the σ = 0 and σ = +1 characters associated with irreducible representations of the group C 3 , and then write a separate Hamiltonian matrix for these two sets in the symbolic form $$true[\begin{array}{cc}center{H}_{RR}& center{H}_{RL}\\ center{H}_{LR}& center{H}_{LL}\end{array}true],$$ where each of the four sub-matrices in Eq. (1) is square, and all four have the same row and column dimension.…”

“…(1) is very similar to the partitioned matrix used in Ref. 15 to treat two interacting sets of torsional levels, one built on the ground vibrational state, the other built on an excited small-amplitude vibrational state. The differences from Ref.…”