使用R中的chron包将一列日期与一列时间组合在一起

I am combining some data to use the match() function to pull specific trade dates/times from a very large data frame and am completely stumped why my code is not working. Notice that the Date and Time columns are separate, which has made a challenge for using the as.POSIXct function as well. Please take a look:I am combining some data to use the match() fun