Gas-phase Raman spectra of hot bands of fundamentals and combinations associated with the torsional vibration of s-trans-1,3-butadiene and its deuterated isotopologues

► Gas-phase Raman spectra of s-trans-1,3-butadiene with unprecedented sensitivity. ► Hot band transitions with the vibrational quantum number up to 8 for ν13 torsion mode. ► Observations of ν13 spacings up to v = 8 in various vibrational excited states. ► Hot bands in Raman spectrum for fundamental transitions that are not Raman active. ► Decreased torsional spacings in almost all vibrational excited states.