adventitiously       
adverb  formal uk/ˌæd.vənˈtɪʃ.əs.li/ /ˌæd.venˈtɪʃ.əs.li/ us/ˌæd.vənˈtɪʃ.əs.li/ /ˌæd.venˈtɪʃ.əs.li/
 偶然地;非计划中地
in a way that is not expected or planned
  A crowd of 5000 people turned adventitiously into an angry mob. 5000人组成的人群意外地变成了愤怒的暴徒。 
 See: adventitious
 - More examples
- It is as if the artist had laid one painting adventitiously on top of another to see what would happen.
- The events are for people seeking to discreetly and adventitiously find someone special.
- The world’s most profitable investment destination is also, not adventitiously, the world’s poorest place.