submitting form in utf_8

How can I ensure that my form submits with characters in utf-8?
The params hash is showing as below though the part "d'\xC3\xA9nergie"
should say "d'énergie"

The text in the input field is set by means of javascript from
clicking an element in a list in a popup.

"treatments_attributes"=>
{"0"=>{"treatmenttype"=>"EDSX,
spectrometrie de rayons X \xC3\xA0 dispersion d'\xC3\xA9nergie",
"prepcomments"=>"",
"preptype"=>"",
"refCoupe"=>"",
"problematique"=>"",
"resume"=>"",
"stock"=>"",
"_destroy"=>""}}}