Touch: difference between 碰，碰觸，觸碰, and 觸
see dictionaries  e.g. bkrs (supplied excerpts restricted to physical touching) 

碰 collide, bump into (4)(of 7) 用手、 脚或器械触及 [bump; touch]。 如: 碰手(方言。 触手、 触疼手); 碰触(接触); 蛇你如果碰它, 它就要咬你 1) touch; knock against
别碰我肩。 Don't touch my shoulder.#2741

碰触 接触、碰撞。
如：「小心，不要碰触电源。」to touch
接触；碰撞。
用指尖轻轻地触碰   

触碰:我们不能触碰法律的底线 触碰一下

触  touch ① 接触；碰；撞：抵触 | 触电 | 一触即发。(6)(of11) 接触 [touch; contact]。 如: 触物(接触景物、 事物); 触桶(便桶); 触冒(接触, 冒着)
to make contact with sth 接触） 
游客请勿触摸陈列品。 Visitors are requested not to touch the exhibits

relevant examples from iciba:碰 他绕桌子走了一圈， 和所有的外宾都碰了杯。碰触 你会颤抖吗 , 如果我碰触你的唇.她伸出手，想去触碰母亲的胳膊。触他第一次触球就得分了

"touch" more commonly(w/o collision) 触摸

interchangeability seems to be a matter of degree, as users can tell in the sense of touching supplied verbs have a high degree of interchangeability, b/c of their other meanings, composition (in case of compounds) they
may convey different flavours

it is also a matter of collocation (搭配)，e.g. for "getting an electric shock " see 触电 above