Neglectfully is the adverb: doing something in a neglectful way — not looking after a person, a duty, or a thing properly, not giving enough attention. You put it next to a verb: they treated the animals neglectfully; the papers were neglectfully left in the rain. English speakers do not use this adverb as often as the adjective neglectful. Though actually, in natural talk people often choose a different shape: they neglected the animals, or they were neglectful, rather than they acted neglectfully. When you do meet it, it is a little formal, the kind of word that appears in a complaint, a report, or a careful essay more than in a chat.

疏忽地、怠忽地（沒好好照顧、或沒給足夠注意的方式）