To quote from the help file for write.table
quote
a logical value (TRUE or FALSE) or a numeric vector. If TRUE,
any character or factor columns will be surrounded by double quotes.
If a numeric vector, its elements are taken as the indices of columns
to quote. In both cases, row and column names are quoted if they are
written. If FALSE, nothing is quoted.
Therefore
write.table(df,"datamod.txt",row.names=FALSE,sep="\t", quote = FALSE)
should work nicely.
