this is obsolete
GetComponent<ParticleSystem>().enableEmission = false;
this doesn’t work because the emission property is read only
GetComponent<ParticleSystem>().emission= false;
and this
ParticleSystem.EmissionModule em = GetComponent <ParticleSystem> ().emission;
em.enabled = false;
doesn’t work because
NullReferenceException: Do not create your own module instances, get them from a ParticleSystem instance
UnityEngine.ParticleSystem+EmissionModule.set_enabled (System.Boolean value) (at <7e14932cc66145488a9440fe43b03616>:0)