Usty-l|) comes at which armonic the bond is break, so the molecule dissociates into atoms. so real molecules behave as an harm oscillator. anharmonic oscillator

yas it's correct you can study in simple form for net exam https://www.dropbox.com/s/sg04374ec7oy4e3/Lecture%205%20Anharmonic%20Oscillator.pptx?dl=0