Anomalous Diffuse Interstellar Bands in the Spectrum of Herschel 36. II.
  Analysis of Radiatively Excited CH+, CH, and DIBs
  Absorption spectra toward Herschel 36 for the A^1Pi <-- X^1Sigma transitions
of CH+ in the J=1 excited rotational level and the A^2Delta <-- X^2Pi
transition of CH in the J=3/2 excited fine structure level have been analyzed.
These excited levels are above their ground levels by 40.1 K and ~25.7 K and
indicate high radiative temperatures of the environment, 14.6 K and 6.7 K,
respectively. The effect of the high radiative temperature is more spectacular
in some diffuse interstellar bands (DIBs) observed toward Her 36; remarkable
extended tails toward red (ETR) were observed. We interpret these ETRs as due
to a small decrease of rotational constants upon excitation of excited
electronic states. Along with radiative pumping of a great many high-J
rotational levels, this causes the ETRs. In order to study this effect
quantitatively, we have developed a model calculation in which the effects of
collision and radiation are treated simultaneously. The simplest case of linear
molecules is considered. It has been found that the ETR is reproduced if the
fraction of the variation of the rotational constant, beta = (B'-B)/B, is
sufficiently high (3-5%) and the radiative temperature is high (T_r > 50 K).
Although modeling for general molecules is beyond the scope of this paper, the
results indicate that the prototypical DIBs at 5780.5, 5797.1, and 6613.6 A
which show the pronounced ETRs are due to polar molecules sensitive to the
radiative excitation. The requirement of high beta favors relatively small
molecules with 3-6 heavy atoms. DIBs at 5849.8, 6196.0, and 6379.3 A which do
not show the pronounced ETRs are likely due to non-polar molecules or large
polar molecules with small beta.
