According to the book "Descendants of Roger Williams" Book III, Sayles Line, p. 305 - 306, this Thomas Arnold married Frances Haynes. However, the date of death in the book does not agree with the RI Cemetery Database, which gives his date of death as 1821; and his wife is Sarah, not Frances.
The only other possibility is that he married Frances first, and that she died in childbirth, in which case the estimated date of birth for their daughter, Anne, must be two or three years off.