I just remembered this novel that I've read ages ago. Basically a 25+ (??) Man and an 18 something women have a moment on opposite sides of an escalator and something sparks when their eyes meet. The guy grabs her hand midway where their escalators meet and asks her to wait at her end for her, then he runs to his end and back to her side and then they have their short introduction and then they decided to get married in court same day. This is a very awkward situation for both cause of the age gap and them being literal strangers but they both decided no to ignore the chemistry between them and chose to pursue it. I think the later part is just them experiencing their marriage without knowing anything about the other party
I know but the MC atleast knew that the ML was a doctor / scientist and married him cause of his prosperous future. In this case, she just randomly marries this guy