A former girls’ soccer coach at a Roman Catholic high school in Western Massachusetts has been charged with asking an underage girl to pose nude for him over the Internet. Michael Dupont of Chicopee was arrested Thursday on a charge of sexual exploitation of a minor. Federal authorities said they started investigating Dupont, 37, in December when a Vermont woman called police in that state to say her 14-year-old daughter had exchanged inappropriate e-mails with a grown man. Dupont is the former soccer coach at Holyoke Catholic High School. The Springfield Diocese said that his contract ended in November and that he is no longer affiliated with the school.