Parsing missing character in filenames as if is reading /

$list1 = @"
quant-ph9802001
quant-ph9802004
"@

$list2 = @"
quant-ph/9802001
quant-ph/9802004
"@

Write-Output "Adding forward slashes"
$list1 -split "`r`n" | % {
    $item = $_.Trim()
    $newItem = $item -replace '(.*)(\d{7})', '$1/$2'
    Write-Output $("{0} ==>  {1}" -f $item, $newItem)
}

Write-Output "Removing forward slashes"
$list2 -split "`r`n" | % {
    $item = $_.Trim()
    $newItem = $item -replace '(.*)/(\d{7})', '$1$2'
    Write-Output $("{0} ==>  {1}" -f $item, $newItem)
}

Function Clean-InvalidFileNameChars {
  param(
    [Parameter(Mandatory=$true,
      Position=0,
      ValueFromPipeline=$true,
      ValueFromPipelineByPropertyName=$true)]
    [String]$Name
  )

  $invalidChars = [IO.Path]::GetInvalidFileNameChars() -join ''
  $re = "[{0}]" -f [RegEx]::Escape($invalidChars)
  $res=($Name -replace $re)
  return $res.Substring(0, [math]::Min(260, $res.Length))
}

Function Clean-InvalidPathChars {
  param(
    [Parameter(Mandatory=$true,
      Position=0,
      ValueFromPipeline=$true,
      ValueFromPipelineByPropertyName=$true)]
    [String]$Name
  )

  $invalidChars = [IO.Path]::GetInvalidPathChars() -join ''
  $re = "[{0}]" -f [RegEx]::Escape($invalidChars)
  $res=($Name -replace $re)
  return $res.Substring(0, [math]::Min(248, $res.Length))
}


$rootpath="c:\temp2"

$rootpathresult="c:\tempresult"

$template=@'
[3]  arXiv:1611.00057 [pdf, ps, other]
Title: {title*:Holomorphy of adjoint $L$ functions for quasisplit A2}
Authors: Joseph Hundley
Comments: 18 pages
Subjects: {subject:Number Theory (math.NT)}
[4]  arXiv:1611.00066 [pdf, other]
Title: {title*:Many Haken Heegaard splittings}
Authors: Alessandro Sisto
Comments: 12 pages, 3 figures
Subjects: {subject:Geometric Topology (math.GT)}
[5]  arXiv:1611.00067 [pdf, ps, other]
Title: {title*:Subsumed homoclinic connections and infinitely many coexisting attractors in piecewise-linear maps}
Authors: David J.W. Simpson, Christopher P. Tuffley
Subjects: {subject:Dynamical Systems (math.DS)}
[21]  arXiv:1611.00114 [pdf, ps, other]
Title: {title*:Faces of highest weight modules and the universal Weyl polyhedron}
Authors: Gurbir Dhillon, Apoorva Khare
Comments: We recall preliminaries and results from the companion paper arXiv:1606.09640
Subjects: {subject:Representation Theory (math.RT)}; Combinatorics (math.CO); Metric Geometry (math.MG)
'@

#extract utils data and clean
$listbook=gci $rootpath -File -filter *.pdf | foreach { New-Object psobject -Property @{file=$_.fullname; books= ((iwr "https://arxiv.org/abs/$($_.BaseName)").ParsedHtml.body.outerText | ConvertFrom-String -TemplateContent $template)}} | select file -ExpandProperty books |  select file,  @{N="Subject";E={Clean-InvalidPathChars $_.subject}}, @{N="Title";E={Clean-InvalidFileNameChars $_.title}}



#build dirs and copy+rename file
$listbook | %{$newpath="$rootpathresult\$($_.subject)"; New-Item -ItemType Directory -Path "$newpath" -Force;  Copy-Item $_.file "$newpath\$($_.title).pdf" -Force}