4. ASTROPHYSICAL IMPORTANCE
It is well-known from the physical and chemical traits of ISM that there
is a continuous circulation of matter and energy at different stages of
cosmic cycle in the ISM. Thus, there is a variation in the molecular
density and temperature within the different regions of ISM. The
low-temperature rotational line data computed in the present study can
be utilized for searching the species in the cold regions of ISM while
the computed vibrational spectroscopic data is quite reliable for search
in the warmer star-forming regions of the ISM. In fact, these are the
probable regions for observing various species being investigated: the
neutral conformers of Leucine, zwitterionic ammonium ylide
(EQ1R1, EQ1R3a, EQ2R3),
imine-diol (EQ1R2a , EQ2R2a,
EQ1R4), and ene-diol (EQ1R2b), similar
to the case of Glutamic acid.33
Also note that in the present work, the rotational database for all the
species is purposely created in lower frequency region than the
frequencies utilized for the search of the simplest amino acid Glycine
in the ISM. In all the astronomical searches so far for Glycine, for
example, in the star forming regions SgrB2, Orion, and low mass
protostar IRAS, the frequency region searched is greater than 80 MHz and
up to few GHz.60–62 However, a high moment of inertia
associated with comparatively larger Leucine molecule and its isomeric
species results into a comparatively lower value of rotational
constants.45 Therefore, it is the lower frequency
region where more intense rotational transitions for Leucine and its
isomeric species can be observed. The lower frequency region becomes
more important for search in dense cold molecular clouds where the
temperature can be as low as 10 K. To assist this, the rotational
spectra simulated for EQ0# with different values of
rotational quantum number J (20-80) at temperature of 10K is
further provided in Figure 4. It can be seen that the frequency range of
10000 MHz to 45000 MHz is the region of high intensity rotational
transitions at 10 K. The higher rotational levels though will also be
get populated as in higher temperature zone but a large number of
transitions from these will be too complex to resolve as can be
concluded using values of rotational quantum numbers:K a and K c (with -J≤ K a or K c ≤ J ).
Therefore, in the present study, the rotational transitions have been
mainly analysed in the frequency range of 10000 MHz to 45000 MHz (with
highest rotational state of J = 30). Nevertheless, the lower
frequency region of this range can act as important aid towards the
laboratory assignment of the transitions whereas the higher range can
directly assist the astronomical observations, for example, through Very
Large Array Sky Survey (VLASS), futuristic lower frequency ALMA Band,
and Square Kilometer Array (SKA).63–65