Объединение ячеек Excel в C#

В общем-то создаю программно Excel файл и записываю в него данные. Как объединить несколько ячеек в одну?

Вот так происходит создание и запись у меня:

    private void CreateExcelDocument()
    {
        excelApp = new Excel.Application();
        FileInfo fileInfo = new FileInfo(Application.StartupPath + "\\" + DateTime.Now.Year.ToString() + " " + DateTime.Now.Month.ToString() + ".xlsx");
        if (fileInfo.Exists)
        {
            excelApp.Workbooks.Open(fileInfo.FullName);
            workSheet = (Excel.Worksheet)excelApp.ActiveSheet;
            curRow = workSheet.UsedRange.Rows.Count;
        }
        else
        {
            excelApp.Workbooks.Add();
            workSheet = (Excel.Worksheet)excelApp.ActiveSheet;
            curRow = 2;
            workSheet.Cells[1, 8] = "Общая";
            workSheet.Cells[1, 9] = "Общая";
            workSheet.Cells[1, 10] = "Общая";
            workSheet.Cells[1, 11] = "Общая";
            workSheet.Cells[1, 15] = "Общая";
            workSheet.Cells[1, 16] = "Общая";
            workSheet.Cells[1, 17] = "Общая";
            workSheet.Cells[2, 1] = "ФИО";
            workSheet.Cells[2, 2] = "Данные1";
            workSheet.Cells[2, 3] = "Данные2";
            workSheet.Cells[2, 4] = "Данные3";
            workSheet.Cells[2, 5] = "Данные4";
            workSheet.Cells[2, 6] = "Данные5";
            workSheet.Cells[2, 7] = "Данные6";
            workSheet.Cells[2, 8] = "Данные7";
            workSheet.Cells[2, 9] = "Данные8";
            workSheet.Cells[2, 10] = "Данные9";
            workSheet.Cells[2, 11] = "Данные10";
            workSheet.Cells[2, 12] = "Данные11";
            workSheet.Cells[2, 13] = "Данные12";
            workSheet.Cells[2, 14] = "Данные13";
            workSheet.Cells[2, 15] = "Данные14";
            workSheet.Cells[2, 16] = "Данные15";
            workSheet.Cells[2, 17] = "Данные16";
        }
    }
    private void SaveAndQuit()
    {
        try
        {
            excelApp.ActiveWorkbook.SaveAs(Application.StartupPath + "\\" + DateTime.Now.Year.ToString() + " " + DateTime.Now.Month.ToString());
            excelApp.Quit();
        }
        catch (Exception e)
        {
            excelApp.Quit();
        }
    }
    private void WriteToExcel()
    {
        int i = 0;
        curRow++;
        i++;
        workSheet.Cells[curRow, i] = RashodMatTextBoxFamil.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 2
        workSheet.Cells[curRow, i] = label123.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 3
        workSheet.Cells[curRow, i] = label124.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 4
        workSheet.Cells[curRow, i] = label125.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 5
        workSheet.Cells[curRow, i] = label126.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 6
        workSheet.Cells[curRow, i] = label127.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 7
        workSheet.Cells[curRow, i] = label128.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 8
        workSheet.Cells[curRow, i] = label129.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 9
        workSheet.Cells[curRow, i] = label130.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 10
        workSheet.Cells[curRow, i] = label131.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 11
        workSheet.Cells[curRow, i] = label143.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 12
        workSheet.Cells[curRow, i] = label132.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 13
        workSheet.Cells[curRow, i] = label133.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 14
        workSheet.Cells[curRow, i] = label135.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 15
        workSheet.Cells[curRow, i] = label138.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 16
        workSheet.Cells[curRow, i] = label137.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
        i++;    // 17
        workSheet.Cells[curRow, i] = label136.Text;
        ((Excel.Range)workSheet.Columns[i]).AutoFit();
    }

Объединить нужно ячейки H1-K1 и O1-Q1, подскажите как это делается программно. Буду очень благодарен