documentclass{article}
usepackage{filecontents}
usepackage{hyperref}

begin{filecontents*}{ref.bib}
@misc{WikiMolecularVibrationHTTPS,
  KEY = {Wikipedia - Molecular vibration},
  TITLE = "{{Wikipedia - Molecular vibration}}",
  HOWPUBLISHED = "url{https://en.wikipedia.org/wiki/Molecular_vibration}",
  NOTE = {HTTPtextbf{S} will textbf{not} work in PDF}
}

@misc{WikiMolecularVibrationHTTP,
  KEY = {Wikipedia - Molecular vibration},
  TITLE = "{{Wikipedia - Molecular vibration}}",
  HOWPUBLISHED = "url{http://en.wikipedia.org/wiki/Molecular_vibration}",
  NOTE = {HTTP will work in PDF}
}
end{filecontents*}

begin{document}
HTTPScite{WikiMolecularVibrationHTTPS}
HTTPcite{WikiMolecularVibrationHTTP}

bibliographystyle{plain}
bibliography{ref}
end{document}