3.1.2 Rotational Signatures in the Isomeric Species of Leucine
All the isomeric species located along the stereoinversion pathways of
Leucine exhibit higher values of dipole moment and hence, exhibit more
intense rotational transitions than the conformers of Leucine. Besides
this, there is a significant variation in the value of rotational
constants among these species, therefore, these can be uniquely
identified. The zwitterionic ammonium ylide species,
EQ1R1, has the highest value of dipole moment followed
by zwitterionic EQ1R3a and EQ2R3 which
can be characterised by stronger b -type transitions in
EQ1R1 and a- type transitions in
EQ1R3a and EQ2R3. The isomers
EQ1R3a and EQ2R3 , despite being
structurally the same, have entirely different rotational parameters,
and hence can be distinctly characterised by their unique (B+C)
transition line patterns associated with a -type
transitions.58
Similarly, the imine-diol-type species, EQ1R2a ,
EQ2R2a , EQ1R4, exhibit their own
characteristic a -type transitions of quite high intensity. To the
contrary, the en-diol species EQ1R2b exhibits strongerb -type transitions.58 The spectral line
database of significant ‘R’-branch rotational transitions for all the
species under study was further created using PGOPHER and is provided in
SI Table S2 of supporting information. Note that in the present work,
rotational transitions were considered only in the frequency range of
10000 MHz – 45000 MHz which are limited to the rotational quantum
number, J ≤ 30. This frequency region actually belongs to higher
intensity rotational transition lines shown in Figure 4, and is
astrophysical quite important as discussed in the next section. Also
note that the line-data in the higher frequency range of 34000 MHz to
45000 MHz, which though is still lower than the typical astronomical
observations, has also been provided in accordance to the highest
frequency band ‘one’ of ALMA.